There was this really sketchy guy at the park, should I call the cops?
Are you sure that the man at the park was acting sketchy?
I didn't see the man long enough to decide if he was sketchy or not, but I suspect he might've stolen my wallet.
If you think that your wallet was stolen by someone, it is a good idea to contact the authorities so that they can investigate that possible crime. If you have good reason to believe that a person you encountered was responsible for the theft, such as them acting oddly, you should mention that to the authorities while they investigate the matter. It's important for the safety of society for crimes to be reported and investigated so that they do not occur again in the future.
I'm going to stay away from that guy.
You should stay away from people if they seem sketchy to you, so that's smart. Next time you see them if you really believe they are dangerous then there's nothing wrong with alerting the authorities.