Apparently from witnesses, and from the audio in the video
Tony Stewart gassed his Car(as you can hear) right as he approached Kevin Ward
to fish tail in Wards direction.
Which he did.
Just so happened that it was too close for intimidation
and he actually clipped him.
Negligence.
It would be negligent if Ward was on a sidewalk and Tony Stewart was on the street. On a race track? Who knows.
In a race, what's more negligent? Applying throttle in a turn or walking amongst the field of racers. In the course of a race, a reasonable driver does not expect to encounter a pedestrian.
At least i'm sure that's what Stewart's defense attorney will say.