The video clearly shows that Marvin put his shoulder in between Bloods shoulder. It's impossible to elbow someone when they are behind you like that.
In fact rather than being a dirty hit by Blood, it was another dirty, intent to injure check by Marvin. If Blood hadn't been ready Marvin would have possibly injured him with another check from behind right in front of the board.
The video is clear. I can't help it that the ability to understand video appears to be correlated with the ability of one's team to win a NCAA tournament game.