From the ESPN story...
Foster had been waiting for an extended period for what the NFL calls his "pre-exam," when he grew increasingly impatient and began questioning a hospital worker.
The hospital worker did not take kindly to Foster's words, and eventually the two were face-to-face, in a heated exchange.
Other players were there at the time, and the NFL is questioning them to get a full account of events.
But one league source said the league has to review the procedures and create better communication so that players understand what is happening and why there are delays.
Sounds like he was just annoyed and let it get the best of him. How bout the balls on that nurse (or whatever he was)? Gotta give it to him for having the nuts to come face to face with a Sith Lord (though that would not have gone well for him had it become more than just an argument).