Watkins Glen, N.Y. Tony Stewart says "there aren't words" to describe his sadness over the accident that killed Kevin Ward Jr.
In a statement released by spokesman Mike Arning, Stewart says "my thoughts and prayers are with his family, friends and everyone affected by this tragedy."
The three-time NASCAR champion hit Kevin Ward Jr. on Saturday night as Ward walked toward Stewart's car following an on-track incident at Canandaigua Motorsports Park.
Stewart says "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."
The decision was an about-face for his racing team, which said earlier Sunday that Stewart would be behind the wheel of his No. 14 Chevrolet when the green flag waved. Regan Smith drove Stewart's car instead.