Colosseum is a Manga/Manhwa/Manhua in english language, ACTION series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

Club Colosseum is a place where criminals who are not properly punished by the law are kidnapped and disciplined thoroughly. However, one of the criminals who was brought in seems slightly different than the others. He escapes the Colosseum and starts a counter-attack on it. Said criminal is Jihoon Ryu, a university student who loves cover and concealment, and someone who has been deemed a criminal for reasons unknown. Follow the action filled revenge story of Jihoon, who turns out to have been a member of the Special Forces in the past!