Why am i so weak in school?

Im in high school year 9 and i weight train everyday and when im at home i feel like im strong but at school when i go to the field and play things like take down bulldog and stuff like that with my Friends everyone just overpowers me and takes me down like im some sort of rag doll. Can someone please help me im sick of being the weak one. P.S I cant take anyone else down either.