Obstruction?

[greymule]

I had a play in which F1 ran toward the 1B line to field a roller, snagged the ball in the webbing, and tagged the batter-runner about two-thirds of the way to 1B.

But the ball came out, and as F1 was reaching across the line to pick it up, the runner tripped over F1's shoe and stumbled, though she didn't fall all the way to the ground. F1 had time then to throw to F3 for the out.

I felt that because the ball was within F1's reach, it was between her and the BR, so the clearly unintentional trip was not obstruction.

But can a fielder with the ball intentionally trip a runner? (Obviously no in Canada, but what about in the U.S.?)