well like if your adc is imobile and you only have CC ways to protect them, then Olaf made a good pick. what you can do is try to fight olaf before he groups, like maybe force his ult defensively. or try to make sure that the adc is safe from everyone else, or make it so that olaf can only focus the adc by running through everyone, which means 3-5 seconds of his ult is used just getting to the adc. as ADC usually if an olaf is comming at me, I just hightail it away from him, even if it means doing nothing but run 'til his ult runs out. I take a lot of damage, but in lategame fights it isn't uncommon that I can use heal one time and flash the next time and it's enough to survive long enough that even if he does kill me it wasted more of the enemy team's resources trying to engage. and, I ping lots if I can, people generally don't always see every player in a team fight so if someone needs help I ping by them, or if an enemy is vulnerable I ping them, and it makes a difference.