Allen, playing behind a makeshift offensive line and receiving his largest workload since the team selected him in the fourth round of the 2015 NFL Draft, carried 22 times for 67 yards and caught five passes for 48 yards in the Ravens' 16-13 win over the St. Louis Rams at M&T Bank Stadium.
"Buck Allen, he played like a pro," coach John Harbaugh said. "He played like a top-caliber NFL running back. You saw it out there. He made guys miss. He made plays in the passing game, plays in the run game. … We just kept hammering, kept banging. We finally cracked a little bit at the end of the game."
Early on, it looked like Forsett would be the one to batter the Rams' front seven. His first two rushes went for eight and 18 yards, respectively, and a 27-yard burst on his next carry was negated by a tripping penalty on guard Ryan Jensen.
Instead, the Rams' front seven ended his season. Defensive tackle Aaron Donald stuffed him in the backfield and threw him to the ground so forcefully that both bones in his forearm snapped when he braced himself on the turf.
Harbaugh said he would be out for the season, and no sooner did Forsett walk off the field with his arm in an air cast did the running game become Allen's domain.
"You've just got to be ready for it," Allen said. "That's what they brought me here for, to be a big-time back."
He'd already carried once for 4 yards before Forsett's injury, but came into his own three series later when he found holes for 21 rushing yards before quarterback Joe Flacco was intercepted. Allen finished the half with 32 yards on eight carries — more than he's had in six weeks — before getting a boost at the halftime break.
In the locker room, Forsett provided the guidance and encouragement to the young running backs surrounding his locker that he has since he arrived with the Ravens before the 2014 season.
"He was in great spirits," fullback Kyle Juszczyk said of Forsett. "I was surprised. It was all in good spirits, and he was just encouraging us. He didn't want anyone to feel sorry for him."
That brief interaction helped spark an impressive second half for Allen.
"It really showed me that he believed in his guys, his backup," Allen said. "He believed in me."
For much of the third quarter, the only plays that offensive coordinator Marc Trestman could believe in were those that went through Allen.
The Ravens ran 44 plays in the second half, with 14 carries and six pass targets going Allen's way. Behind an offensive line that by the midway point of the third quarter included three reserves (left tackle James Hurst, left guard Ryan Jensen and center John Urschel), Allen ran 14 times for 35 yards in the second half.
His greatest contribution came in the passing game. Allen wasn't targeted before the half, but finished tied for the team lead with five catches and had 48 yards. Many of the catches sparked drives. On third-and-2 at the edge of field-goal range in the fourth quarter, he took a short pass 14 yards for a first down to set up the Ravens' first touchdown, a 3-yard pass to receiver Kamar Aiken.
He was spelled on a few carries by Juszczyk, but otherwise was the team's sole running back. Juszczyk said Allen "made the most of his opportunity."
"He's someone that we've learned to rely on here recently," Juszczyk said. "He's done a really great job. He's committed to getting better every day, and you see it on Sundays."
Allen, in all likelihood, will assume the lead role in the Ravens running game with Forsett out and second-year back Lorenzo Taliaferro on injured reserve following Lisfranc foot surgery.
The only other active running back Sunday was Raheem Mostert, an undrafted rookie who was claimed off waivers from the Miami Dolphins in October. Mostert, the team's kick returner, did not have an offensive touch in the game.
Allen said he's ready to take on whatever role the team needs.
"If that's something I'll have to do, then I'll step up and do it," Allen said.