How tight your fists should be?

[Lissove]

When I strike I try to keep my hands open and close my hand into a fist when I strike. Does it matter how tight it gets or if you closed it properly, and what is q properly closed fist? My thumb gets left outside and not overlap at the bottom, I try to turn my fist inward too. It's easier with boxing gloves as you can't form a proper fist in the first place, and the strikes aren't as fast, but with MMA gloves the strikes are so much faster and you get all the available space from them,so a lot of opportunity for strikes, I feel I am not using what's available to me because I can't close my fist in time to strike. I don't even strike because I think I won't close my fist in time for that.

 

[ARIZE]

My thumb gets left outside and not overlap at the bottom

That's a huge NO. You can literally destroy your hand that way.
For the rest, the others will probably correct better than me, but for the thumb thing, don't do that...

 

[a guy]

This video will change your life:

 

[Silver tongue samurai]

I would say usually you want to make as close to a fully closed fist as possible. Duane Ludwig promotes corkscrewing your hand at the end of a punch to hit with the first two (power) knuckles. Someone mentioned to me if you want to hit lighter striking with an un-clenched fist would achieve that. As for closing them in time I dont think you should worry about that, just throw and try to tighten the fist as close to impact as possible you want to be loose up until the point you connect