When someone grabs the collar of your shirt, what would you do? You might often see that the victim grabs the collar of the attacker who grabs the collar of his shirt first. Then both start pulling the shirt and saying to let it go.
It is a common scenario. You can do different things to defend yourself against collar grabs. Your hands are free while the attacker grabbing the collar of the shirt. You can directly strike him if you want.
You can also release the attacker's hand from the collar of the shirt and then strike him. Let's watch this video. You can follow this as well that showed in the video.
There are situations where you do not want to hit the attacker, but you have to defend yourself. So what can you do? You can simply grab the attacker's elbow that grabs your collar and move it up. Move behind the attacker while grabbing the elbow up.
The attacker is not grabbing the collar of your shirt anymore. Now you can move him out of there and get rid of that. Whatever you do, you need to consider the situation you are in. Sometimes you just cannot do something because of the situation. So you need to adapt to the situation and make your move accordingly.