Interference?

[bossman72]

Had this happen the other day:

R2. Batter hits a grounder to F6. F6 charges and catches the ball. His momentum then takes him a couple steps towards home where he sets to throw. Just as he cocks his arm back, R2 crashes into him. R2 really didn't have much time to react. I called him out for runner's interference.

I then thought about it and have this question:

I know the fielder is protected from fielding a batted ball, but once the ball is fielded and before he throws it, does he have the same type of protection? Was my call right?

Thanks

bossman