Allen believed it was a clean play.
"I turned around, he was running to make a tackle and I threw myself into him to make a block," Allen said, via The Associated Press. "My condolences to him and his family. I never, ever, try and intentionally hurt anybody."
It's true that Allen doesn't have a long history of fines related to hits to the head. He was fined in 2008 for a low hit on Houston Texans quarterback Matt Schaub. So we'd expect Allen to receive a hefty fine for this hit, although a suspension wouldn't make sense because he's not a repeat offender.
We contacted the NFL for comment on Allen's hit but have yet to hear back.