The Indy 500 is the biggest event in motorsports and, for many racing fans, an excellent chance to win some cash.

Last year, Alexander Rossi won as a mammoth 80/1 underdog. Anyone who bet on the rookie cashed big.

Before you bet Sunday's big race at the Brickyard, you'll want to hear what ex-Vegas bookmaker Micah Roberts has to say.

When everyone else wasn't backing Rossi (15/1) last year, Roberts was all over him to finish in the top five, and it paid off in a huge way.

This year, Roberts thinks a driver who's getting 50/1 will finish in the top 10 and make a run at the title. He could be this year's Alexander Rossi.

Roberts called Juan Pablo Montoya (12/1) winning the Indy 500 twice. In 2000, he scouted the Vegas IndyCar test session and pegged Montoya, who was a 15/1 underdog, to win it all.

After watching qualifiers and analyzing the field, Roberts, who helped popularize betting on auto racing, finalized his 2017 Indy 500 picks and listed where he believes all 33 drivers will finish.

One driver he's not high on is three-time Indy 500 champ Helio Castroneves (10/1). Roberts thinks Castroneves barely cracks the top 10 and finishes ninth.

Will pole-sitter Scott Dixon win the Indianapolis 500? And what huge underdogs will finish in the top five and make a run at the checkered flag? Visit SportsLine now to see Roberts' pick to win the Indy 500 and find out.