Twenty-one college football head coaching jobs opened by the end of last season, continuing the trend of the highly active coaching carousel on an annual basis. A ton of jobs have changed hands the past few years, and it's inevitable that there will be a big wave of switches this November and December, again.

So, as the 2017 season nears, let's take a look at the coaches in each conference who are under the most pressure to win. This is not necessarily a list of coaches who are on the hottest seats and most in danger of losing their jobs; not every conference has a true hot-seat coach. It's a conference-by-conference guide to which coaches most need big seasons or improvement to ease pressure that exists now or could quickly build if things go wrong.

ACC

Most pressure: Dave Doeren, N.C. State. Doeren is in a brutal situation. Put N.C. State in the ACC Coastal, and it might be the division favorite. In the Atlantic, however, the Wolfpack have to deal with a preseason playoff favorite (Florida State), the defending national champion (Clemson) and the team with the defending Heisman Trophy winner (Louisville). They also play at Notre Dame and vs. South Carolina in Charlotte, and they draw Pitt and North Carolina from the Coastal. It's a difficult schedule for a coach who has struggled to win big games. Doeren is 25-26 in four years since leaving Northern Illinois; worse, he's 9-23 in ACC play. Of course, had a late field goal been made, N.C. State would have beat Clemson last year. He did at least help himself by beating UNC to end last regular season and attain bowl eligibility. With an excellent defensive line and an experienced offense, the hope is that N.C. State can pull off a surprise or two and aim for a winning record in ACC play for the first time since 2010.

Others: The ACC has made some great coaching hires in recent years, upping the potential for a conference riding high right now with two national titles in four years and the reigning Heisman winner. The hottest seat beyond Doeren belongs to Boston College's Steve Addazio, who desperately needs to put a more watchable product on the field. He's 24-27 in four years with teams that have ranked 70th, 86th, 121st and 118th in scoring, and the university just hired a new athletic director.

Big 12

Most pressure: Kliff Kingsbury, Texas Tech. Kingsbury is an all-time great Texas Tech player, the first prolific Air Raid quarterback under Mike Leach, setting the stage for a decade of success. Texas Tech badly wants this to work. But four years as head coach have been a struggle for the 37-year-old Kingsbury, even with offenses continuing to crank out absurd production -- and No. 10 overall draft pick Patrick Mahomes. Kingsbury is 24-26. Since Kingsbury has arrived, the Red Raiders are 11th in total points scored … and yet they have a negative point differential in that time. Mahomes threw for over 5,000 yards last year and Texas Tech scored 43.7 points per game, but the team finished with a 5-7 record. In the past two seasons, Texas Tech has four losses in games in which it scored over 50 points. Now, Mahomes is gone and top receiver Jonathan Giles transferred to LSU. The Red Raiders desperately need to improve on defense after finishing 125th or worse in points allowed in three straight years.

Others: Contract uncertainty and middling results had put Dana Holgorsen under pressure at West Virginia, but he won 10 games last year and signed an extension in December, so he is now on stable ground in 2017. With that situation settled, nobody is under immediate pressure like Kingsbury, so we'll just say Tom Herman at Texas, because the Longhorns are desperate to win, and win quickly, after the mediocrity of the Charlie Strong era.

Big Ten

Most pressure: Mike Riley, Nebraska. Riley is entering only his third season. He is not on the hot seat. Nevertheless, in a conference mostly made up of either proven coaches with job security or relatively new hires -- thus putting no one truly on the hot seat -- Riley is under the most pressure. After all, he's 15-11 in two seasons at Nebraska, which fired Bo Pelini after eight seasons in which he had a .713 winning percentage. The Cornhuskers are in the weaker Big Ten division in the West, but they haven't played in the conference title game since representing the Legends Division in 2012 before the Big Ten was reshuffled. Riley's first season in 2015 was filled with bad luck; last year, the Huskers started 7-0 but lost four of their final six games, including a 59-point loss to Ohio State and a 30-point loss to Iowa. Nebraska has not won a conference championship since the Big 12 in 1999. There will perpetually be intense pressure on whomever the coach is to snap that streak.

Others: Again, everybody is either on stable ground or a new hire. There is a different sort of pressure on Mark Dantonio at Michigan State, though. He's been one of the greatest coaches in school history, with a 90-42 record and three straight AP top-six finishes from 2013-15. He is, however, trying to rebound from a sudden 3-9 downturn, in a brutal division that includes a powerhouse Ohio State, an energized Michigan and a revitalized Big Ten champion Penn State. It's hard to shake the feeling that a golden era in East Lansing is over.

Pac-12

Most pressure: Jim Mora, UCLA. The Mora era has shown flashes of potential, but ultimately it's the same old story of unrealized potential for UCLA. Mora went 20-6 in 2013-14 with back-to-back top-20 finishes -- the first time the Bruins did that since 1997-98 -- and they appeared in the Pac-12 title game his first two seasons. But last year's team collapsed to 4-8, with a broken offense. Prized QB Josh Rosen missed the second half of the season with a shoulder injury, but the offense was a mess before that thanks to a stagnant run game and lackluster offensive line. Mora let go of offensive coordinator Kennedy Polamalu after one season and hired Jedd Fisch to try to capitalize on what is likely the final college season for Rosen, the five-star recruit who's expected to be a first-round NFL Draft pick. With rival USC bouncing back to the top of the Pac-12, Mora needs to quickly prove that last year was an anomaly.

Others: Coaching tenures shouldn't be judged by one game, but it's not hard to see a scenario where pressure is heightened around the battle for the Territorial Cup on Nov. 25. Arizona won the Pac-12 South in 2014, but since then the Wildcats are 10-15, plummeting to 3-9 last year. Making matters worse for coach Rich Rodriguez, athletic director Greg Byrne left for Alabama. At rival Arizona State, Todd Graham has struggled to put together a defense that can stop anyone. The Sun Devils are 11-14 the past two years and allowed 39.8 points per game in 2016. The two rivals finished a combined 3-15 in Pac-12 play last year and don't want to miss the postseason in back-to-back years.

SEC

Most pressure: Butch Jones, Tennessee. The Volunteers are stuck playing Alabama in a cross-division game every year, but nobody in Knoxville is going to accept yearly losses to Bama as a reason to not win what's been a historically weak SEC East. Florida teams with lousy offenses have backed into the SEC East title the past two years, even after Tennessee finally ended an 11-game losing streak against the rival Gators. That was supposed to be the launching point to a breakthrough season, with a veteran roster expected to push the Vols to the SEC title game for the first time since 2007 and a top-10 finish for the first time since 2001. Instead, the Vols finished 22nd in the AP poll, again, a comeback-fueled 5-0 start proving to be unsustainable as they finished 9-4 with losses to Alabama, Texas A&M, South Carolina and Vanderbilt. Jones promoted tight ends coach Larry Scott to be the new offensive coordinator, and the Vols have to rebuild without players like QB Josh Dobbs, WR Josh Malone, RB Alvin Kamara, DE Derek Barnett and CB Cam Sutton. Strong recruiting results mean that the Vols still have the talent to compete for an open SEC East title, but patience is wearing thin for a program that has had a four-loss ceiling for more than a decade.

Others: The entire SEC West. That includes Nick Saban, because there's always ridiculous pressure on Saban to win, but really it's everybody else in the division who is stuck competing with the absurd standard that Alabama has set. Gus Malzahn needs to get Auburn's offense back on track with the help of Baylor transfer QB Jarrett Stidham and new coordinator Chip Lindsey. Kevin Sumlin and Texas A&M need to stop collapsing in the second half of the season. Bret Bielema is 25-26 overall and 10-22 in the SEC in four years at Arkansas. Ed Orgeron is trying to prove he was the right choice for LSU. Dan Mullen is trying to ensure that Mississippi State didn't already peak with Dak Prescott. Perhaps worst of all, Hugh Freeze is coming off a 5-7 season with an NCAA scandal hovering over Ole Miss.

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Independents: Brian Kelly, Notre Dame. Things change quickly at Notre Dame. In 2015, Kelly pulled off a fantastic coaching job, as the Fighting Irish survived terrible injury luck to win 10 games and go to the Fiesta Bowl, losing only to teams that finished that season ranked No. 2, 3 and 4 in the AP poll. Last year, however, Notre Dame collapsed. Defensive coordinator Brian VanGorder was fired after a rough start, and the Irish finished 4-8 with seven of their losses by eight points or less, including to Navy, N.C. State and sub-.500 Texas and Michigan State teams. Kelly has a new offensive coordinator (Chip Long) and a new defensive coordinator (Mike Elko). He lost QB DeShone Kizer but has a promising new signal caller in Brandon Wimbush. Beyond Wimbush, the biggest key is developing the defense. The pressure is intense as Kelly enters his eighth season with three top-25 finishes in seven years and a 59-31 record. The close losses meant plenty of bad luck last year, but the Irish have to turn things around against a schedule that has the potential to be difficult, including Georgia, Miami, Stanford, Michigan State, N.C. State, North Carolina and Navy, among others.

American: Major Applewhite, Houston. Nobody is on the hot seat in the American. There are 12 coaches in the conference, and only Navy's Ken Niumatalolo, who was hired in 2007, has been head coach of his school for more than two seasons. He is in as stable a position as any coach in the country. The conference has established itself as the launching point for rising star coaches, with USF's Willie Taggart and Temple's Matt Rhule making the leap this year. (UConn and Cincinnati also fired their coaches.) After Niumatalolo, the next-most experienced coaches are SMU's Chad Morris and Tulsa's Phillip Montgomery, who are entering their third season. So who is under the most pressure? Perhaps it's Applewhite in his debut as he replaces Tom Herman. He beat out defensive coordinator Todd Orlando for the job, with other big names like Lane Kiffin and Les Miles mentioned. Houston is trying to be a Big 12-caliber program in the American, and it doesn't want its recent Herman-built cachet to disappear along with him.

Conference USA: David Bailiff, Rice. The actual answer might be Lane Kiffin, because there has never been a bigger spotlight on Florida Atlantic. But in terms of needing to win more games now, the answer is clearly Bailiff, who is 56-69 in 10 years coaching the Owls. While Rice won 10 games in 2013, things have gotten progressively worse since then, falling to eight wins in '14, five win in '15 and a disastrous three wins last year after a 0-6 start.

MAC: Paul Haynes, Kent State. Kent State has no reason to be anything but patient. After all, it has played in one bowl game since 1972, when Nick Saban was a senior defensive back for coach Don James. The one bowl bid was in 2012, when Darrell Hazell had an 11-3 season and vaulted to Purdue. Haynes replaced Hazell and has gone 12-35 in four seasons, including 3-9 last year. The MAC East is the conference's weaker division, but Haynes has won only eight conferences games, with particularly rough performances on offense.

Mountain West: Matt Wells, Utah State. Another case of nobody truly being on the hot seat in the conference, thanks to changes made at San Jose State, Nevada, Fresno State and Hawaii in the past two years. Wells won 19 games in his first two years upon replacing Gary Andersen. He's 28-25 overall with three bowl appearances at a school that had two winning seasons from 1981-2010. So let's not get carried away -- Wells is in no immediate danger. Still, in the competitive Mountain Division in which Wyoming and New Mexico have had turnarounds, the Aggies have gone in the opposite direction, falling to 6-7 in 2015 and 3-9 last year. Utah State wasn't as bad as its record indicated last year and it should improve, but a bounce-back season is sorely needed.

Sun Belt: Doug Martin, New Mexico State. Poor New Mexico State. The Aggies haven't played in a bowl game since 1960, and they're about to be kicked out of the Sun Belt, on their way toward independence in 2018. (Idaho is also getting kicked out but will drop to FCS.) Martin is the latest to struggle with one of the most difficult jobs in sports. When Martin got the job in 2013, the Aggies hadn't won more than four games in a season since 2004. They still haven't, as he's 10-38 in his four years, with one more left before New Mexico State tries to make independence work.

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Contact Matt at matt.brown5082@gmail.com and follow him on Twitter @MattBrownCFB and Facebook.