In my opinion — the key player.
This spot can make or break a team, more than a skip or a lead. I find that you really need to have the right player to fill this spot and perform this job. Think of this role as your navigator. He is the middle-man between the Skip, who is calling the shots and laying out the tactical game plan, and the front end who are the engine to your ship and are laying the foundation.
This spot is key for playing a lot of shots to help the team out. They draw to add to the head or even to save the head, they are the first runs at conversion shots (if the opposition is up), they are advising the Skip on the situation, they measure and are the ones who normally declare a head, they are the encouragement for the front end when the skip is at the other end.
If you think of the Skip as the manager, then the third is the supervisor or the assistant manager. They don’t usually deal with the “big picture” but are the ones doing the nitty-gritty to get things done. They are the first ones to try conversion shots, they are the ones dealing with the front end and keeping them happy and they do this for the team as the Skip should be focused on more of the game than micro-managing the team.
Normally I would hold this position for someone who is technically the best bowler, they may not have the best leadership or the best tactical ability, but they should be able to bowl the lights out. They should be a confident draw player as they often need to draw in a shot or a second shot to save the head. They should have a great drive as they will often be called to attempt the drive so the Skip can either have a clearer shot or an easier shot to save the end.
They need to have a grasp on tactics and on efficient information. Poor thirds can often have no idea what to do or what to tell the skip or on the flip side they can sometimes take over the game and try to justify their position by ordering the skip on a shot or undermining them with what they believe is best. The best thirds can give information, give advice and call a head if required but also know the skip is the leader and know when it is appropriate to voice their opinion.
I also like a third who has a great eye for angles and for measurement. If you have a third who can confidently tell you who the shot bowl is on a tight measure, then you have a great advantage on playable shots. If you make the wrong decision and play a shot that hurts you because you didn’t know who was shot it can kill a game.
— Parts taken and paraphrased from Evan Tanzer’s article for the Corinda Bowls Club