FIFA 17 – How to Perform a Driven Throw with the Goalkeeper

Here's my suggestion, based on the actual circumstances that earned me the Specialist achievement.

Play defense on pl_badwater. Make sure your team has a few competent damage sponges (Heavies, Soldiers, and Demomen) who know how to retreat (you may need to explain that bullets are hazardous to your health).

You want to stay alive. You can facilitate this by always sticking to a buddy. The best buddies to stick to are the ones that hang around sharp corners near narrow corridors:

In these locations, you and your buddy can stay behind cover in the yellow area, and once they are fully healed (to 150%, conditions permitting), they can venture into the red zone for ideal damage exchange along the highlighted lines of sight (where Heavies, Soldiers, and Demomen have a captive audience, so to speak, of the cart's escorts).

Note that the general advice here (be on a good team, play against a bad team, heal everybody) still applies, and that you'll still need classes like Engineers (who can help by putting dispensers near you) to cover your back.

When you're sprinting, with the hookblade equipped, tap B (or O for PS3) right as you approach your target. If you HOLD the button, you'll only do a hook and run, which isn't what you want. It takes a little practice to get the timing right, but it's pretty fun when you do it right. Side note: It doesn't seem to work on Janissaries. They always manage to avoid the "throw" part.