"A lot of people don't think I'm athletic, but I didn't use to weigh 280 (pounds)," said Petrus, who's actually closer to 290 pounds. "I used to weigh like 225 back in high school, so when I gained all this weight, I kept some athletic ability."
Petrus knows he can't run or change directions like Darren McFadden or Felix Jones, but frankly, he doesn't have to. All the 6-foot-5, 288-pound sophomore needs to do is get into position quick enough to block for Arkansas' star running backs.
At many schools, a change at fullback wouldn't be that big of a deal, and the guy who replaced the starter wouldn't get several interview requests in one week.
But Arkansas' offense is based so heavily on McFadden and Jones running the ball that the fullback position has become even more important.
And with starter Peyton Hillis sidelined with a severe thigh injury, and backup Farod Jackson still limping because of an ankle injury, the No. 5 Razorbacks don't have many options at fullback for Saturday's 1:30 p.m. game at Mississippi State.
It's between either Petrus, who was expected to be a backup offensive guard this season, and freshman Ben Cleveland, the former Springdale High star who has played tight end and wide receiver this season.
There is a chance that Jackson could be ready by Saturday, but for the time being, Petrus is considered the starting fullback and Cleveland is his backup.
"At the beginning of the year, that's kind of what (the coaches) wanted me to play was fullback," Cleveland said. "They moved me to tight end, and they moved to receiver.
"They had it in mind the very beginning of the year (for me to play fullback)."
Cleveland is versatile because he's 6-foot-4, 235 pounds and can catch the football, as well as block. And there is a chance that a few passes could be thrown the freshman's way on Saturday.
In the one snap that Cleveland played fullback as a senior at Springdale High, he caught a short pass from quarterback Mitch Mustain and ran for a 62-yard touchdown in a 42-14 win against Bentonville.
"Ben is an athletic guy that you can move around, and he has done some of that (playing fullback) in high school," said Arkansas offensive coordinator Gus Malzahn, who coached Cleveland at Springdale High.
Cleveland and Petrus have worked in practice this week to prepare for replacing Hillis in the lineup, though that could be tough to do considering Hillis has made key blocks this season to set up McFadden and Jones for long runs.
Hillis, who has been bothered by a deep thigh bruise since the season started, had to be taken to the hospital following Saturday's 31-14 win over No. 22 Tennessee because of severe swelling in his right leg.
Arkansas coach Houston Nutt has ruled Hillis out for this week's game, and there is a chance that the Conway native could miss even more time because of the thigh injury.
"He's been banged up pretty good, and his leg is pretty swollen," Arkansas running backs coach Danny Nutt said. "So hopefully, we can get him back by next week."
In the meantime, Petrus and Cleveland will try to handle the fullback position. Petrus will be used mostly on run-blocking, and Cleveland could go in on pass plays, where he could be a target to catch a pass.
"It's definitely not a sorry position," Petrus said of playing fullback. "You have an important job, and if you don't do it, you're going to get pulled because you have to do it to be successful."
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