Sunday afternoon's 49ers win over the Cardinals saw its share of extra-curricular activities that will cost players some cash. Alex Boone was fined $7,875 for his personal foul against Cardinals defensive lineman Alameda Ta’amu. At the same time, Ta'amu is being fined $10,000 for stepping on Boone. My guess is the fine is actually $10,500 based on this schedule of fines.
The series of plays was detailed in a helpful GIF at The Big Lead. Boone was fired up and dropping f-bombs in the first two GIFs. The third GIF shows some of the development of the play. Boone is down and Ta'amu seems to have a hand on him. I don't know that he's necessarily holding Boone down, but we see Boone swipe at Ta'amu's helmet. That is followed by Ta'amu getting up and stepping on Boone with his right foot.
In looking at the GIF, it could be purposeful, but I also think you could see how Ta'amu might have lost his balance a bit and that it might be an accident. There's another Cardinals lineman on the ground and Ta'amu appears to be trying to step around him. I'm sure plenty of people here will disagree with that interpretation, but I don't think that is entirely out of the realm of reality.
Whatever the case, both men are appealing the fine. Boone was flagged for a personal foul, while Ta'amu was not flagged. I believe Boone's personal foul was for something after he was stepped on, but I'm not positive.