"Most big kids when they play football in junior high and high school are prone to be nice, take it easy," said Bob Buckel, O'Brien's coach at Powers Catholic High in Flint, Mich. "That's what sets Danny apart. He's really aggressive for his size. He's scary. I know he's run into me on the practice field a few times and I've feared for my life. He's a very aggressive kid."
That aggression made O'Brien a 4-star prospect in Scout.com's ratings. It made him the most celebrated commitment to date for Tennessee's 2012 signing class. It also made him a target for opponents looking to land cheap shots.
"Danny got cut-blocked at the knees a lot," Buckel noted. "In one game he got cut and went down hard. Before the trainer could get out there, though, Danny came hopping off the field on one leg. He motioned that he was OK so play wouldn't stop with us trying to run out the clock in a crucial game. Instead of worrying about his knee, he's worried about getting to the sideline so the clock won't stop."
O'Brien packs 302 pounds on a 6-foot-3 frame but his heft may not be his greatest attribute.
"He's pretty athletic for someone that size," Buckel said. "He started for our basketball team last year and he also played fullback for us, scoring five touchdowns this year."
Still, O'Brien's future is at defensive tackle, not fullback. He sealed that deal by posting 68 solo tackles, 28 assists and 4 sacks in 14 games as a senior.
"Danny's a big force in the middle of our defensive line," Buckel said. "He often draws triple teams, which allows our linebackers to make tackles because they're not blocked as often as he is."
O'Brien projects to make immediate impact on a Tennessee squad that is coming off a 5-7 season and desperate for team leaders. A devout optimist, he set the bar high during Powers Catholic's first weight workout following the 2010 season.
"He set the goal for the team to be state champs, which was interesting since the team was coming off a 1-8 season," Buckel said. "But Danny's very motivated, very goal driven."
And he's very true to his word. With O'Brien providing the impetus, Powers Catholic rallied from a 2-4 start to win its final eight games. The last was a 56-26 beat-down in the state finals of previously unbeaten Lansing Catholic, a squad that had trounced Buckel's team 37-17 in September. Reportedly, it marks the first time in history that a team coming off a 1-8 season won a state championship.
Although O'Brien is best known for his abilities as a run stuffer, he has serious potential as a pass rusher, too.
"He's basically a bull pass rusher because he's bigger than most of the kids he plays against," Buckel said. "He's been to so many clinics and camps that he has fantastic technique. He only had four sacks this year because he's usually getting cut by smaller people trying to knock him off his feet. I think he'll do well in college facing players his own size."
Another factor that could make O'Brien a better player at the college level is the fact he'll concentrate on one sport. While most of his football teammates were lifting weights last winter, he was helping Powers Catholic's basketball team reach the state quarterfinals.
"He's very strong in his upper body and likes to work out in the weight room," Buckel said. "He's a kid that bench-presses 220 pounds probably 15 to 20 times. But all last winter he was on the basketball team, so we didn't get him lifting until March."
Given O'Brien's tremendous upside, The Vol Nation is eagerly anticipating his arrival on The Hill. The feeling appears to be mutual.
"Danny's fired up about getting to Tennessee," Buckel said. "He's a pretty passionate player."