The Trip

[so cal lurker]

Curious about something after watching the appalling trip in the Jets game . . .

The dolphin is running out of bounds on his way up the field -- is that legal? I thought (and I know I'm not a rules expert) that players always had to stay on the field, not run along the sidelines outside the boundary. What is the rule?

(And no, I'm not in any way suggesting that it makes the trip any less reprehensible . . . at least the Jets are taking it seriously and taking action against the behavior . . . )