"연습 방송중이던 벵기선수" => 연습 방송 중이던 벵기 선수. Player [Contestant] Benggi who was doing a trial broadcast. - 연습: practice, trial, preliminary run. - 방송: broadcast. - ~ 중이다: is in the middle of something; be doing something. - ~ 중이던: (who) was doing something. (이)던 describes an activities that was in progress in the past. - 벵기: a person's name. - 선수: a player, an athlete, or a contestant in a competitive event.

Player Benggi who was practicing LoL over the air 연습 방송 중이던 벵기선수 is actually short for 게임연습을 방송중이던 벵기선수. I don't know whether you know who is Benggi. He is a professional gamer in League of Legend and He's name is 배성웅. Benggi is his player name. Many of pro-gamer in Korea broadcast their practice matches on some applications, such as Africa TV, Daum pot TV, etc.