Leon was a bookie, keeping tabs on most of Gotham's sports betting.
History
Leon grew suspicious when a series of sporting events were ending up as farces due to the preferred contenders freaking out in fear, particularly because he was paying a lot of winning bets to a mysterious new gambler. This had also come to Batman's attention as he was investigating the fixed games and saw that Leon had been "taking it on the chin" after all these lopsided victories. After paying off a big bet, he wondered exactly who this bettor was, who jokingly called himself "Mr. Lucky", but Leon secretly had one of his goons follow the gambler with the intent finding out what his secret was, completely unaware of the gambler's true identity. The goon, of course, did not come back.