Can’t the commissioner punish any player, team, etc for conduct detrimental to the league? Including fines & forfeiting draft picks?
While there has been intense backlash at the Ravens for backing out of the Maxx Crosby trade, there's really no recourse to the Raiders or the NFL:
Even when trades are official, they often have conditions that are negotiated, including a player reporting to a new club and passing a physical by a certain date. The result of a physical is at the discretion of the new club’s doctor.