Also what muscles do you use most while playing rugby. PS: I'm 13 years old. I play number 8 I'm 5 foot 10 Any answers are great

Hi Conor I have never heard of kettelbell, so you probably know more than me. But I do know about rugby. If you are a 5'10" 13 year old, I suggest you should consider that lock would be more useful in your team than No. 8. For that, you need upper body strength, so I guess any exercises that increase that would be good. If you remain as No 8, you need speed and agility, more than strength.