Olivier was pushed into a corner by the other two. Every time he tried to step out of his range and fire back, Mark had his path blocked by a taunt.
That disruption in game flow was enough for Dan to take advantage of an attack Olivier back. It was an ongoing back-and-forth between them both.
If Olivier wanted even to have a chance of winning, he needed to make sure that his opponents were divided and did not get to cooperate. And Olivier even had a plan for achieving this.
The first thing Olivier did was change his attack targets. He could not do anything against the shooter since Dan was well-hidden and protected by his partner. So Olivier took a shot at the tank.
Mark had not expected that sudden change in pace and was caught off-guard. That gave Olivier enough time to set up an advantageous position.
Even Dan could not hit once Olivier regained his footing.