Just finished a 12u rec game. Batter hit a slow weak ground ball to SS. SS fielded it and made a bad throw into the dirt to the home base side of 1st. 1st baseman went after the ball falling over onto her hands and knees in the process with her legs/butt blocking the baseline and upper body into foul territory. She didn't catch the ball, but did knock it down. She was able to pick up the ball and reach back to tag the runner. To avoid the collision our runner checked up and ran back to the inbound side of the baseline. Because the runner hit the brakes and had to run around her, the 1B was able to get the out. The runner clearly checked up and had to deviate from the baseline before the 1B had the ball. Ump argued that the fielder had the right to go after the thrown ball and it wasn't obstruction. I thought that only applied to a batted ball? I don't want the encourage our players to intentionally run over another player at full speed, but is contact needed to get the obstruction call? The 1B was in a pretty compromising position and could have gotten hurt if our player ran across her legs or put a knee into the girls ribs going if she went over the top of her.