I figured you meant something more subtle than a big red flashing light, but here's the thing:
A) The difference between a clean hit and a dirty one is a matter of milliseconds. Players who dish out the hits can do very small things at the very last moment to try to hurt an opponent and I don't think any sort of warning system will help you with that. The time needed to react is way too long and you would need to be able to detect 'malice' in someone's intent, which is not exactly easy.
B) Pro sports players are known to hate additional equipment, gizmos, protection extras, etc. even if it means reducing their own safety. Hockey players get hit in the face with sticks and pucks going 100 mph all the time, but still prefer to not wear a visor because they find it "more comfortable". They don't care if they're completely toothless (they actually see this as an honor - many don't get work done until they retire), as long as they can play unobstructed. Same with braces and pads, players will never wear them (and players' associations will side with them) if it means gaining half an inch on the pitch.
Unfortunately, I don't think any amount of technology will help here. We need to change the way people think about contact sports (someone in this thread mentioned its likeness to wresting) and change the rules to protect the players better.
The dislike of face protection isn't that dissimilar to their complete dislike of helmets 20 years ago. The old pros made excuses, the younger player that grew up wearing them became pros that wear them, now they all do.
Cycling also had that same thing,I think it was Andre Kivilev's death that turned it around. I can't remember that last time I heard apro complain about helmets in cycling. PBR bull riders are also rapidly embracing helmets and face guards. The cultures of these sports can rapidly change, the players don't want to be maimed when it's all said and done.
The bigger issue, honestly, fans want to see violence and the leagues want to please the fans and make money. Media surrounding the nfl has sold videos of big hits, they used to have a segment on the Sunday pregame on ESPN called "jacked up." The nhl isn't terribly different with fighting, games that aren't mass broadcast are different, if the score becomes too far out of balance it can become a different sport altogether. Lots of talk about teamwork, the sacrifices, the incredible strategies and tactics (aspects of football are beautiful and fascinating) but ultimately it's not much more than gladiator fighting.
> but ultimately it's not much more than gladiator fighting.
In Australia, where I'm from, there is a NRL match between Queensland and New South Wales called "State of Origin". One of the key draws for it is the "grudge match" in-group bias that comes along with it, and the very high probability of big fist-fights breaking out (which they do, with regularity, though less so the past few years).
It's also one of the biggest games of the entire year. Those two things are not unrelated.
I get that as well that is why I say the NFL would have to force it. I played football in high school and did get my fair share, I can only imagine the speed increase at college and NFL.
Some indicator would help get past the problem of the helmet obscuring player sense. Assisting the player back to the feeling of not having a helmet while they do, in terms of peripheral vision sense, behind you and around you would be nice. If you don't have a helmet on and someone rushes up behind you in a game they are easier to see without a helmet. Just knowing someone is there is enough to prevent concussions. It is the blind shots where someone doesn't expect it that can really cause problems. Head on collisions usually aren't as bad because of both players awareness. If there is some way to inform the player of players around them within a range I think would help immensely and if it is very out of the way the players would deal, especially the previously concussed.
It could be some pretty cool tech, almost drone/neural network like combined with gaming elements connecting player helmets and pads (they do have some indicators tracking players on shoulder pads now - http://mashable.com/2014/07/31/nfl-shoulder-pad-sensors/). But I agree it would have to be forced on the player by the NFL only, no team or player would do it without the NFL forcing the changes. Awareness of players on the field is one of the biggest deterrents to concussions, anything the NFL can do to help that would be good for their case.
In hockey, there's the additional element of the incremental penalty for being the aggressor in a fight while wearing a visor. So, "enforcer" players choose not to wear a visor...
Rule 46.6 in the N.H.L. rule book: “If a player penalized as an instigator of an altercation is wearing a face shield (including a goalkeeper), he shall be assessed an additional unsportsmanlike conduct penalty.”
A) The difference between a clean hit and a dirty one is a matter of milliseconds. Players who dish out the hits can do very small things at the very last moment to try to hurt an opponent and I don't think any sort of warning system will help you with that. The time needed to react is way too long and you would need to be able to detect 'malice' in someone's intent, which is not exactly easy.
B) Pro sports players are known to hate additional equipment, gizmos, protection extras, etc. even if it means reducing their own safety. Hockey players get hit in the face with sticks and pucks going 100 mph all the time, but still prefer to not wear a visor because they find it "more comfortable". They don't care if they're completely toothless (they actually see this as an honor - many don't get work done until they retire), as long as they can play unobstructed. Same with braces and pads, players will never wear them (and players' associations will side with them) if it means gaining half an inch on the pitch.
Unfortunately, I don't think any amount of technology will help here. We need to change the way people think about contact sports (someone in this thread mentioned its likeness to wresting) and change the rules to protect the players better.