Ray Rice will appeal his indefinite suspension by arguing the NFL based it off a cleaned up, edited version of the security tape from a Revel Casino elevator, according to a report by ESPN's Adam Schefter. Rice was released by the Ravens, then suspended indefinitely by the league after TMZ released video from inside the elevator showing the running back throwing a punch and knocking out his then-fiancee, Janay Palmer.
The argument Rice reportedly intends to present is one of semantics:
Legal sources told Schefter that the TMZ tape of Rice hitting his then-fiancee was a cleaned-up, whittled down and condensed version of the events that took place in the Atlantic City casino elevator.
*The tape is edited heavily for clarity, and this is noted by TMZ in its original post. The raw video TMZ used as source material is here.
This implies that Rice will argue there were circumstances that provoked him to knock out his then-fiancee, and that the NFL didn't take those circumstances into account when re-disciplining him. This would also imply the video of the punch in itself wasn't enough evidence to warrant an indefinite suspension. The fact that Rice threw a punch powerful enough to knock his then-fiancee unconscious is not in dispute.
Also of note, former FBI director Robert Mueller will get the full tape of the incident for his independent investigation. The NFL couldn't, or didn't even bother trying to, get the tape when looking into the matter over the course of months, but Mueller will have full access to everything now. Only took seven months.