Sometimes, people just won't go away. They nag, they annoy, and they persist. Proper conflict resolution says we should walk away or talk about the issues at hand, but this is America, and sometimes it's easier to just shut the offender up with a shot to the jaw, and when Shepard makes his or her point, we listen.
Paparazzi are annoying to begin with, sure, but when one of them is plainly trying to smear Shepard's good name, even after continued attempts to be civil, sometimes physicality is inevitable. We're not sure we wouldn't act the same way, given what Al-Jilani was trying to do. We don't normally condone random face-punching, but we can't help but sympathize with Shepard here.