Ex-Boxing Champ Arrested -- Allegedly Tried to Join ISIS

Former British boxing champ Anthony Small -- who was 23-2 as a pro -- is on trial in England for allegedly trying to sneak off to Syria to join ISIS ... this according to the BBC.

The 33-year-old boxer was arrested in England along with two other men after authorities say they were trying to forge documents to illegally enter Syria.

Small and the two men have all been charged with engaging in conduct in preparation of terrorist acts -- though Small DENIES the allegation.

Small most famously fought in "The Contender Challenge: U.K. vs. USA" in 2007 -- when fighters from the U.S. reality show "The Contender" flew to England to fight up-and-coming boxers, including Small.

Small defeated Walter Wright, who competed in Season 2 of the boxing reality show.

Small converted to Islam at the age of 24 -- and in 2012, he made a YouTube video in which he said he quit boxing because the sport took place in venues that Muslims are forbidden to enter because of gambling, alcohol and half-naked ring girls.