Is this a foul to you?

[ranjo]

A1 is dribbling from the division line in his front court on an angle toward the left side of the paint. He is being guarded by B1 who is matching him step for step. There is very minor foot to foot contact, A1 loses his balance and goes down, the ball rolls out of bounds. I decline to call a foul because I couldn't determine that either player did anything out of the way to cause the contact and rule it incidental. A1's coach questions the play and I ask him if B1 was the player to go down would he expect me to call it on his player. That caused him to stop and ponder the answer while I quickly put the ball back into play.

I know it is usually a foul on the defense when the offense gets tripped up, but in this case, do you think it should have been called.