Tyler Walker (VPS Motorimages Photo)

Tyler Walker, a driver in the NASCAR Craftsman Truck Series, has been suspended from competition indefinitely by NASCAR, for violating the sanctioning body's substance abuse policy.

On May 18, Walker was found to have violated Sections 12-4-A (actions detrimental to stock car racing) and 12-4-E (failure to comply with the NASCAR Substance Abuse Policy) of the series rule book.