My spar ratio is 495-463 I think. I'm not the greatest but I can still give you tips from what I've learned while sparring.
1.) ammo - You want something that has a great clip because if your magazine is too small, you will find yourself often reloading and that's when your opponent can take advantage of you. A good weapon for spar that has a good magazine is the Sten. The Sten has a clip size of 32.

2.) heading to the bottom of the map - When the spar battle begins you want to instantly make yourself go to the bottom as fast as possible. How can you go fast? Try going diagonally, that's the fastest way to move.

3.) Once your at the bottom - Once at your bottom you want to spam and make a wall of bullets preventing your opponent from being able to control the bottom. After a while, your opponent might try to go to the top. When that's the case you want to shoot up and down and also move yourself towards him to make sure you don't get cornered. This is why it's good to have a big magazine size because once you reload, they can possibly run fast enough to the bottom and then the tables will turn. Once that happens, you can be in jeopardy in losing.

That's really all I know.

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of losing*******