"Do you play sports on the weekend?"
やる is the dictionary form. It is an う-verb, not a る-verb. You can tell it's not a る verb because they normally have いる/える endings (たべる。 みる。 there are some exceptions which are still う-verbs, such as 切る(きる).
When putting an う-verb into ます form, you bump the う into an い。
So やる becomes やります まつ becomes まちます のむ becomes のみます
When you're turning a る verb into ます form, you just drop the る。 たべる becomes たべます みる becomes みます ねる becomes ねます
Does that make any sense at all? I'm not much of a teacher haha.