SlimGauge |
Pathfinder Maps Subscriber
The "free" means "without additional action cost", not "free from potentially provoking an AoO".
What is giving you the free Bull Rush attempt ?
If it comes from Shield Slam, that specifically says the free bull rush doesn't provoke.
If it comes from the Piledriver(Ex) that a Foehammer gets, that also specifically says that it doesn't provoke.
What specific case are you looking at ?