This time it's because Casey Pachall is hurt.
Boykin led three straight scoring drives after Pachall left with an injury, and the Horned Frogs pulled away from Southeastern Louisiana 38-17 on Saturday.
Pachall, who missed most of last season after an arrest on suspicion of drunken driving, injured his left forearm at the end of a running play late in the second quarter, didn't return and was ruled out of TCU's Big 12 opener at Texas Tech on Thursday night.
"Probably not good," TCU coach Gary Patterson said, declining to offer any specifics. "He won't play next week. I can promise you that."
Boykin played the final nine games in 2012 after Pachall was arrested and went into a substance-abuse program. Pachall returned in the spring, and the quarterbacks split time in last week's opener against LSU. They were even both on the field for the first play, with Pachall under center.
Pachall had taken just about every snap before he was injured Saturday, and Boykin had the first three catches of his career before Pachall got his arm caught under a couple of defenders as he was tackled along the sideline.
While Pachall walked slowly to the locker room, Boykin ran 16 yards on the next play, and Jaden Oberkrom ended the first half with a 46-yard field goal that put the Horned Frogs (1-1) ahead 17-14.
Boykin completed a 29-yard pass to Brandon Carter on the first play of the second half, and Carter finished that drive with a 5-yard scoring run. Then Boykin threw 27 yards to Josh Doctson for a 31-14 lead.
"I pretty much knew the game plan and I tried to execute it and play within our system," said Boykin, who was 3-6 as a freshman starter a year ago. "It wasn't that difficult to do to come in after Casey had the injury."
Bryan Bennett had 132 yards passing and another 132 rushing for the Lions (1-1), who were even at 14-14 late in the first half despite never scoring more than 10 points in five games against BCS teams since bringing back football in 2003 at the FCS level.
"I love his competitive spirit," Southeastern Louisiana coach Ron Roberts said of the Oregon transfer who also had two interceptions and lost a fumble. "I think that's the big thing that allowed most of our guys to feel comfortable coming in here, to follow him and know that we felt we had our opportunities and our chances to win."
Boykin's first play at quarterback was a handoff to Waymon James for the game's first score, a 1-yard plunge. B.J. Catalon followed his kickoff return for a score against LSU with a 51-yarder to start the game and had a 15-yard scoring run. He led TCU with 59 yards rushing.
Pachall guided a pair of scoring drives and finished 8 of 14 for 100 yards. Boykin was 9 of 13 for 133 yards and two touchdowns and added 35 yards rushing before he was replaced by third-stringer Tyler Matthews late in the game.
"He just makes some plays with his legs that Casey hasn't, but Casey makes some plays with his arm that Trevone doesn't do," Patterson said. "But it's two weeks in a row he came in and did some good things."
Bennett had a 45-yard run to set up the Lions' first touchdown, and threw a 65-yard scoring pass to Jeff Smiley to pull even at 14 late in the second quarter.
It was a bit of a shocker considering Southeastern Louisiana had been outscored 272-26 in five previous games against BCS teams going back to 2006.
"I think it kind of gives us a little, not hope, but it shows us how good we could really be," Bennett said. "To be able to compete with a Top 25 team like TCU shows us that we were right there with them."
Facing the Big 12's best defense from a year ago, the Lions had 207 yards rushing a week after they picked up 309, their most since the program's return.
Defensive end Devonte Fields played the second half for TCU after missing the first game and a half as part of a two-game suspension for an unspecified violation of team or university policy during the offseason. Fields had one tackle.
Patterson had said he wanted to get Fields some playing time before the Big 12 opener at Texas Tech on Thursday night. Fields still must serve another half-game suspension.
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