The NFL player protests have become very much like PETA's nude magazine ads or when streakers run naked at sporting events in support of different causes. All are shocking acts meant to command people's attention towards a given issue. But this strategy fails because the intended message is obscured by its delivery, which becomes a spectacle, while the original message is forgotten.
I wouldn't consider the NFL protests a fail, given that we literally have a commentator on FOX news taking prime time to accurately describe to the audience "this is why they're protesting".
Judging by the reaction, most people who they are trying to reach out to - those who don't already feel that police brutality is a serious problem - are being pushed away. I don't think I've heard anyone say 'you know what, I didn't think police brutality was an issue before, but now that these players are protesting the anthem, I'm inclined to agree with them'.