In their first four games, the Pistons have been hampered by foul trouble, sidelining some of their starters in the first few minutes and throwing coach Stan Van Gundy’s rotation into further flux. It’s notably happened to Avery Bradley and Stanley Johnson — the Pistons’ best two perimeter defenders — and they’ve had trouble finding a good rhythm on the defensive end. They looked forward to having both of the wings to wreak havoc; instead, they’ve been relegated to early time on the bench. What’s worse is that it’s been putting the opposition on the free-throw line at an alarming rate, pushing the Pistons to the bottom of the league in a couple of defensive categories. “We’re leading the league in fouls, we lead the league in free throws allowed — and they’re not from being physical,” Van Gundy said Tuesday. “In fact, a lot are from not being physical — we slap and reach instead of moving your feet and getting your body in front of somebody. Slapping down on a guy going to the basket instead of staying vertical and taking contact in the chest. “It’s not like we’re this really physical; we’re getting a lot of bad fouls and it’s something we need to correct.” Part of the issue is Van Gundy’s insistence this season on playing a more in-your-face defensive style, pressuring the ball more and not allowing ball-handlers to get easy passing lanes or to attack with drives to the basket.