Basketball turned to karate with a little less than two minutes remaining in the first quarter and Memphis leading 25-13. Paul split the defense at the top of the key and took off toward the hoop, sucking in Allen from the left wing. Paul head-faked Allen off of the ground, and the Grizzlies guard spread both his arms and legs to attempt a would-be steal. Paul maintained possession, though, and kept his course toward the hoop until Allen's left leg contacted him squarely on the left side of his head. Paul staggered backward but he did not fall, and he eventually flung the ball backward as he reacted to the direct contact.
The referees initially assessed a Flagrant Foul 1 but that was upgraded to a Flagrant Foul 2 upon video review. The Flagrant Foul 2 designation is given out to fouls that are deemed both "unnecessary and excessive" and it carries an automatic ejection. Allen reacted as if his kick was unintentional, but it's a little difficult for Allen to argue that it was "necessary" for his leg to be more than five feet off the ground, even if the contact was incidental. The NBA has taken a hard line against blows to the head in recent years and that's almost certainly what earned Allen his ejection. If the kick lands on Paul's shoulder this is likely a different story.
Following Memphis's 106-102 victory, Allen apologized to Paul on Twitter.
Allen departed with five points (on 2-for-4 shooting) and one rebound in 10 minutes. Paul was able to continue playing following the unusual foul.
Here's an up-close, animated version of Allen's kick to the face.
Both Paul and Allen were selected to the 2013 All-Defensive First Team last season. GIF via @CJZero