A few random musings.

1) Given a PC with a Broken Leg...

If it makes it harder to dodge, that's providing passive opposition.

If you stumble on it as you dodge out of the way, that's an invoke.

If you can't climb a ladder, that's narrative truth

If there's a ladder between you and where you need to be, that's a Compel.

2) While not always or necessarily true, I've noticed GMs tend to provide event compels while players provide decision compels.  The GM affinity to events is probably higher than the player affinity to decisions.