As Texas A&M's season spiraled from College Football Playoff contention to not even in the New Year's Six bowl mix in the span of a month, one of the reasons for the struggles was the decline of the Aggies' defense.

A unit that was at times dominant in the first half of the season was anything but down the stretch. More than two weeks after a regular season-ending 54-39 loss to LSU and some time to reflect on the downfall, Aggies' coach Kevin Sumlin said fatigue might have played a key role in why it happened.

"We played more snaps than any other team in the SEC on defense," Sumlin said. "With that being the case I think we were worn down towards the end of the year."

Not only did the Aggies lead the SEC in number of defensive snaps, the unit was on the field for more plays than any team in the Power 5: 974. Oregon (971 plays) and Texas (955), two other teams that struggled defensively, ranked No. 2 and No. 3, respectively, among Power 5 teams in defensive snap total.

Texas A&M's total defensive play count was the third-most in the FBS this season behind only South Florida (1,000) and Middle Tennessee State (995). Seven times this season the Aggies defense was on the field for at least 80 plays.

"Our rotation system was not what we needed to do," Sumlin said. "Injuries are part of the game, so that’s not an excuse. We have to find a way in many critical situations to get off the field on third down. We didn’t do that well enough. Those problems continued to snowball as the year went on, playing that large number of plays.

Over their final four games, Kevin Sumlin and the Aggies were among the worst teams in college football at stopping opponents on third down. Kevin C. Cox/Getty Images

"You look back as a coach, the first thing you say is 'Well your offense wasn’t able to keep your defense off the field.' That’s not necessarily true. You take a team like Ole Miss, who had less time of possession than us ... throughout the year, but still played almost 80 [defensive] snaps less during the course of the season than our defense did. Our ability on third down has got to get better."

Ole Miss' defense was on the field for 891 snaps this season, and had only three games when it was on the field for more than 80 plays.

As for that third-down defense? The Aggies -- who face Kansas State in the AdvoCare V100 Texas Bowl on Dec. 28 -- allowed third-down conversions at a 39.2 percent rate, which put them in the middle of the pack nationally (65th). However, the difference from the first eight games (when the Aggies went 7-1) and the last four (when they were 1-3) was a stark one. In the first eight games of 2016, the Aggies allowed third-down conversions only 34.3 percent of the time. After Nov. 1? That rate shot up to 49.2 percent, which ranked 113th out of 128 teams in the FBS in that time span.

And that inability to get off the field keeps drives alive and thus, adds to the opponent's play count.

"We’ve had some discussions about two things; we’ve talked about schematics and we’ve talked about personnel," Sumlin said. "Some things that were problems schematically that have been addressed, and some things from a personnel standpoint that we’re somewhat limited in that game and the number of plays that our guys were on the field. It’s not just one thing. It’s a combination of a lot of things that really manifested itself at the end of the year.

"We have to get off the field on defense on third down and eliminate basically playing almost two more games than the average team in our league, and those snaps added up, and ultimately, created some issues for us the last few games."