Being the underdog
But what if your opponent has control over armor and shield?
He will have an armor advantage, so you should avoid direct fights, donīt take any risks. If you run towards him and start shooting you can as well type suicide in the console.
All you can do now is to slowly wear his armor down. There are several ways to do that.
You can snipe him from the distance.
You can shoot around corners with Flak/Grenades/Ripper.
You can do guess shots with the ASMD/RL.
Something else you can do is wait for him to get you. You should wait somewhere where you have positional advantage, for example at the top of an elevator or at a position with height advantage.
You could also sneak to the armor once he leaves it or wait for him at the shield with a defensive weapon like ASMD/RL/Flak.
A bit more risky is to try ambushing him. He will have to go from armor to shield and back to armor once a minute (Phase I and III), thatīs where you try to get him. You just hide somewhere between armor and shield and as soon as he runs by you shoot him in the back with a strong weapon like Flak, Bio Rifle, Sniper, ASMD or RL.
If he is a good player though he will know the hiding places and make guess shots. Thatīs why itīs such risky, if that happens you are dead meat. But if you are able to surprise him you can easily kill him. 6 flak shrapnels in his back, a combo, a big slimeball or a sniper hit and his shield is gone, so you just have to finish him of or retreat to the armor/shield, whatever respawns next.
Most important is that you still keep track of the shield respawn times, even if you donīt get it. You could for example wait somewhere near the shield, to hear the pickup sound or you just substract another 55 seconds to the last spawn time, pretending, that he picked up the shield just as it spawned and calculate with that time.