Athletes always know each other

So I'm just watching the Cleveland/Boston Basketball game and I see LeBron and Marbury hug each other. Do these guys really know each other? One's like 24 the other's 31? It's like this with all the athletes it seems. I understand some might live close to each other or know each other from past teams, but not everyone can know everyone. They see each other 2-4 times a year, no way are they that close. I don't even hug my sisters. I'm just taken aback by it. Athletes must be really friendly people. Now the mystery is why they're always involved in shootings?