force play slide rule?

[ggk]

ncaa.
R1, 1 out. slow roller to F5. he fields the ball and throws to F4 who catches the ball for the force. F4 is standing on the back of the bag - left field side - when he catches it. there was no way that he was going to have a chance to make a play at first and made no indication that he was going to throw to first. R1 slows down going into 2nd, but does not slide and his momentum carries him forward and he makes slight contact with F4. he does not knock F4 down or do anything malicious. he clearly did not alter the play as there was no additional play being made.

i was BU and I had nothing. i stayed with the play at 2nd as there was no throw being made to 1st. PU called interference because R1 did not slide or avoid F4.

is this a violation of FPSR?? any difference in FED??

thanks.