NOTE: This strategy shows how to defeat Borys using the Dodge Counter maneuver. If you have not yet unlocked the Dodge Counter skill, you can still beat him, but it takes a little more effort. See the main walkthrough for details.
When you ride the zip line down to the Endurance, Lara lands in a stack of iron pipes and hunkers down as she hears voices ahead. Move forward to the opening, hop down...
...and quickly take cover behind the wooden crate so the men working on deck don't see you. There's a bundle of arrows here. Borys, the big man whom you may have heard the Solarii on Shipwreck Beach mention, moves to help the man on the right with some cargo. Wait until he says, "Out of the way...I got this," and starts moving the load with his rope ascender.
Use this opportunity to take out the man on the left with a silent headshot.
As Borys works the rope, you can then kill the second normal-size man the same way.
Borys will notice this and stop working. He's not the sharpest knife in the drawer, however, so most of the time he'll take a moment to bend over and look at one of his fallen comrades. If you like, you can try and target him with a headshot while he's distracted. This won't kill him, but it will shave off a little of his health.
Then jump out into the open so you have room to maneuver. If there's time, try and get around behind Borys...
...and shoot him in the head once or twice. His sturdy armor protects his body, but his head is vulnerable. Don't worry if you can't do this. The main thing is to move into the open so he can't corner you and get ready to fight.
Once he notices Lara, Borys will move toward her with his fists raised to protect his head. You can't hurt him now, but keep a weapon trained on him. I like the shotgun for close combat, but use your favorite.
Let him come to you, and when he lunges toward Lara, dodge his attack by continuing to hold Aim and pressing Dodge/Roll (Shift/Circle/B) while simultaneously moving to the left or right.
If your dodge is successful, the Melee icon appears on screen, just like in the quick time events. Press Melee (F/Triangle/Y) in time with the prompt (i.e., wait for the gray circle to to contract into the inner ring and the Melee icon to appear, then press the button).
If you press the button at the right time, you'll see the Dodge Counter icon flash briefly on screen.
You don't need to press a button now. Lara will automatically stab Borys in the leg with an arrow, knocking him off balance briefly.
Now you regain control. As Borys struggles to remove the arrow, shoot him in the head as many times as you can. Repeat this process several times, incapacitating him with the Dodge Counter maneuver, and then shooting him in the head.