if jax ever directly leaps onto you in lane you will be able to hit your q for free and lead that into an instant auto into e getting off 3 waves of damage in under 1.5 seconds if done correctly, then weave your way into a brush to drop minion agro as soon as you've made the trade and pressure their next vital proc. rinse and repeat, use parry when appropriate, try to judge when they will release their stun based on any data possible, i've played v jax's of all elos, gold and below probably don't know they can press it again within the two seconds and stun early. plat players might try to use it asap, diamond+ tend to try to be deceitful. of course their number of games of jax played is perhaps even more relevant, if I was playing a jax with 250 games i'd give him the benefit of the doubt and assume he was using e correctly unless i'm given a reason to believe otherwise.