It's just 2 gaming terminology words combined, (throwing and trolling), mostly used when a relevant situation can be described by throwling instead of saying both throwing and trolling.
For those of you who doesn't know
Person 1: I feel like this guy is intentionally whiffing his shots and wants to sabotage our team.
Person 2: nah man, he's more like throwling in our team no cap.
Person 1: I guess so, yeah.