when you are gambling without making group
"Group betting" could mean anything, someone could be part of the syndicate or maybe just two friends placed a bet on the same game.
The other question is even if someone is part of the syndicate, how can sportsbook have any real condemning evidence of that?
CoinPlay sent some evidence to Askgamblers:

Didn't work.
when you are not doing arbitrage betting
I don't think any of these sportsbooks mention arbitrage in their TOS. Nevertheless...
NBA game Washington Wizards vs Detroit Pistons.
Sportsbook A offers Washington Wizards 2.02
Sportsbook B offers Detroit Pistons 2.02
If I bet 1000$ on both teams, I'm making 20$ either way.
But how can Sportsbook A have evidence that I placed the opposing bet on Sportsbook B? They can't. It's all speculation on their part.
I was expecting a response, perhaps response with anger from GekkeBelg but he seems gone or have no idea about the topic but it seems you and Martingaleboy so far are doing the job for him.
You are advocating for a world where the sportsbooks have the ultimate power to freeroll everybody, without showing any evidence.
I'm just advocating for a world where sportsbooks honor their bets.