Being overwhelmed

If you're sparring somebody 30 lbs heavier than you, then even blocking all his punches will tire you out. The legs are working extra hard just to maintain balance, let alone keep from getting knocked around off balance.

But, being the smaller man, you might have an advantage in speed. Especially leg speed.

So a good idea might be to move around a bit, side to side, and preemptive head movement to make him look for you, rather than you reacting to slip his shots. That'll keep you one step ahead of him.

And after you get comfortable with his timing and start making him miss, then counter to the body first. This will be your best bet to slow him down fast.

If you get into a situation where he's right on top of you, get low, clinch him around the waist and slide around him to his side. No sense in wrestling with a bigger man. You can even make him use his weight to your advantage by feinting the upper body to one side and immediately stepping out the other way. So if he's got you on the ropes, shift the upper body to the left and put your weight on the left foot, then use the momentum of the left foot to move right as you roll under and step with your right foot, to the right, and exit around him. If you get real comfortable with that, you can even get a punch off as he's turning back to face you.

You can also try it the opposite way. Feint the upper body like your moving to your right while putting weight on the right foot. Use the momentum of loading the right foot to roll under while stepping to the left and then pivot out around him. Immediately smack him with a right hand from the side.

 

First of all why would you spar some 30 lbs heavier then you? If its not for drilling purposes then i dont see the point.
Your legs are your best asset so you will have to move a lot and change angles often plus good body shots will tire him out. After a while usually the brawlers settle and then you cant coordinate you attacks better without fear of him constantly attacking.