NASCAR driver who killed opponent under investigation

The incident leading up to the tragedy appeared nothing out of the ordinary.

Three-time NASCAR champion Tony Stewart and Kevin Ward Jr tangled, with the latter's car ending up on the barrier.

But then, a clearly agitated Ward left his car, walking onto the track to confront an oncoming Stewart.

That's when the 20-year-old was struck and killed, during a race in New York.

Local police are now investigating.

Already, however, the American media is rolling out Stewart's list of race-track priors.

They included his own eerily similar incident in his rookie year of 2009.

In 2011, he was arrested by Sydney police after an altercation with the owner of the Parramatta raceway.

Last year, there were fisticuffs with a rival driver.

Today, as Stewart withdrew from a Nascar event in New York, he issued a statement via Twitter which read: "There aren't words to describe the sadness I feel about the accident that took the life of Kevin Ward Jr".

Meanwhile, in the event Stewart bypassed, several drivers were lucky to survive a horrifying crash.

As their vehicles crumbled around them, the drivers were merely shaken up by the collision.