If you can prove that there is a history of game-time burglaries in that parking lot, and convince a court that what the stadium did in response to that history was not reasonable, then you might be able to recover for whatever losses you can prove. This is absolutely not a do-it-yourself lawsuit, even if it could be brought in small claims court.
Whether you file a claim against the insurance is up to you. If you do, you need to understand that you are putting your friend's job at risk.