If something is off chance, it is very unlikely to happen. "Oft" is an informal abbreviation for "often".
The expression "oft chance" is incorrect.
"Off chance" is correct.
JaVale McGee Vine’d himself giving $100 to someone sleeping on the sidewalk (Video) On the off chance that you didn't have your eyes glued to JaVale McGee's Twitter account at around 7 p.m. Eastern on Thursday, here's what the always colorful Denver Nuggets center shared with the world — a six-second video of … Continue reading ?
June 14, 2013 - Ball Don't Lie via Yahoo! Sports