Zac has really long cooldowns on his engage abilities. Because of this, he can only really use them as an engage or escape tool once per fight. If you know he is without these abilities- try to fight him.
Placing vision around his jungle entrances and in the river will reduce his ability to get successful ganks off. Take note that Zac can gank from afar with his E though.
The easiest way for Zac to kill the Scuttle Crab is by using his E . If you see him killing the Scuttle Crab, it will usually mean that his E is on cooldown and he’ll lack an escape tool.
Zac’s E can be used from afar to start the team fight. Make sure you ward your flanks when sieging an objective.
Avoid fighting in the jungle as it will make it easier for Zac to land his E and knock up your whole team with his Ultimate R. Fight in the open when possible.
Do not group too closely. If you’re split up slightly, it will be impossible for Zac to catch out and knock up your whole team with his E and Ultimate R.
Zac can gank at level 2 or 3 depending on which ability he went second. Expect him to gank your lane at level 3.
Zac is really good in team fights as his kit has tons of CC. Try to disengage whenever he E’s in to make it harder for him to get a good knockup.
Once Zac hits level 6 and unlocks his Ultimate R, his gank and kill pressure increases. Expect him to look for or force ganks once his Ultimate R is up.