WordNet (r) 3.0 (2006):

sporting chance
    n 1: a reasonable probability of success [syn: fair chance,
         sporting chance]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "sporting chance":
   best bet, blind bargain, chance at odds, favorable prospect,
   gambling chance, good chance, good opportunity, good possibility,
   likelihood, main chance, matter of chance, odds-on, odds-on chance,
   possibility, potluck, potshot, probability, random shot, sure bet,
   sure thing, toss, toss-up, touch and go, well-grounded hope