lol I read that if you have the rocket launcher and you fire one straight at him when the level starts. He'll grab it and you just get your partner to shoot the rocket and then he'll run away.
Or something...
I dunno I haven't done it yet I'm still working on getting my Infinite Ammo Rocket Launcher :p
I've never tried firing at him with a rocket once the fight starts, but doesn't he dodge at the beginning even if you fire right away with a gun? So I'm thinking he'll dodge an even slower rocket....
The only time you can hit him is if his back is turned, or when he's charging up to sprint at you.
And actually, it takes 2 rockets to make wesker retreat, in all modes (pro, vet, etc)- which are also stackable (one rocket to make him hold, and another rocket to fire at the rocket he's holding). The quickest way I've found to beat wesker (with infinite rocket launcher) is:
* when the fight starts, run straight towards jill, have one person restrain her, than have the other do the throw context command, which will knock her out for i believe 30 seconds.
*after jill is knocked out, have one person head straight to the door (the door wesker kicks you through) while the other person (with the rocket launcher) stays away; but READY (i.e launcher equipped and with a good view, preferably a straight view, to the door)
*have the person at the door taunt, as taunting provokes all enemies, including wesker. if the 1st taunt doesnt provoke, keep stacking it. this will initiate the door kicking sequence.
*immediately after the sequence, have the person with the rocket launcher fire at wesker (whom which by the way has his back turned). he should grab the rocket, which opens him up for the 2nd rocket!
*wesker will be brought down to his knees, and all you have to do is wait till he recovers, and he will take off runnning...
That whole process is less than a minute! Beating wesker without the rocket launcher is a lot more fun though!