Stewart was racing in a dirt-track race in New York, when he hit the on-foot driver.
Ward, Jr. was pronounced dead on arrival.
Stewart was supposed to race in Sunday's sprint cup series at Watkins Glen.
Regan Smith raced in his place finishing 37th. While A.J. Allmendinger won the race.
Stewart released a statement saying, "There aren't words to describe the sadness i feel about the accident that took the life of Kevin Ward, Jr. It's a very emotional time for all involved, and it is the reason I've decided not to participate in today's race at Watkins Glen. My thoughts and prayers are with his family, friends and everyone affected by this tragedy," said Stewart.
"He was visibly shaken by this incident and has promised his continuing cooperation in this investigation. There are no criminal charges pending at this time. This is an on going investigation," said Ontario County Sheriff, Philip C. Povero.
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