Board Thread:Questions and Answers/@comment-205.213.134.253-20140122154854/@comment-66.193.171.226-20140221202426

The answer to this is very simple, whichever character will deal the most base damage for the match, will be the one attacking. So, simply look at the blue damage for each character, and whoever is the highest will do the attack. So, that means Black Widow needs to be leveled up high enough that her Blue damage is higher than anyone else on the team (in order for her to make the attack on a blue match).