A car mechanic is not the car owner who watches an actual car mechanic fixing some car.
A problem solver is not CEO of a company who just watches an actual worker solving a problem.
A football superstar is not the #1 fan sitting in the front row watching someone's ingenious moves.
Players play. Players do not just watch, read or facebook (ingame cutscenes are an exception). Players do not wait for others to do something, players bite, players fight.
Next video case is made by a player (it's not the first time I'm adding this vid, sorry). I'm a player too as I played this game, and I admit I wasn't even close to this skill.
Some, not players but watchers, will never admit they "no can do". What's even worse, they'll live in delusion it's exactly the way and exactly the efficience how they'd (be able to) play this game. And their own impression about playing a game will come from mere imagination instead of actual experience.
Finally, some games are designed to be fun to watch but a chore to play. Movies and TV shows are designed to be fun to watch too.
But watching all that still makes you a watcher. Not player.