Against braum, Braum doesn’t have the best of sustain in the early game. Try to harass and poke him down whenever he tries to last hit minions. If you can keep him low, he’ll never be able to engage.

In team fights, avoid standing too close together as it will allow him to knock multiple champions up with his Ultimate r. Group but do not stand super close together.
 
The longer the game goes the tankier Braum gets and the stronger his ADC gets too. Try and set him behind in the early game to make it harder for him to peel for his ADC as the game goes along. Against braum, Braum does not have the best to support in the early game. Try to harass him and bring him down every time he tries to last hitting minions. If you can keep him low, he will never be able to engage. In the team fights, avoid being too close together as this will allow him to hit several champions with his Ultimate r. Group but not stay super tight together. The more the game goes the Braum tankier gets and the stronger his ADC becomes. Try and place him behind in the early game to make it harder for him to peel for his ADC while the game is going on.