What classification of foul? and pre-game Uniform rules.

[Y2Koach]

Tournament game prior to my team playing. B1 is pressuring A1 as A1 dribbles up the court. As A1 is crossing half court, A1 slips and loses the ball. B1 picks up the ball and is about to start heading towards his basket for an uncontested layup when A1, laying on the ground, grabs B1 by the foot to foul and prevent the layup. Official calls a foul, team B inbound from the side.

After the game, as my team is warming up, I ask the officials why it was not called intentional foul as no play was made on the ball. The officials proceded to walk from me without answering, and about 2 minutes later, interupted our layup line to tell my players to tuck in their jerseys (shooting shirts still being worn on top of jersey, and a good 7 minutes before game time).

Would you guys have called an intentional or just a common foul? Are there rules about jerseys being tucked in during warmups?