I'm loving my 7D2 and 70-300L for outdoor soccer. One son plays defense and the other is a keeper so I can usually set up at mid-field and cover most of the action in the defensive third of the field. I haven't had a chance to shoot any outdoor tennis yet, but I'm confident this combo is more than up to the challenge.
My problem will be this Fall when my older son(the defender) plays varsity soccer under the lights. Then he'll transition to indoor track for the Winter with some indoor tennis matches sprinkled in to tune up for the Spring outdoor tennis season. I know I'll need a faster lens, I just don't know which one I should buy. This is for personal use only, nothing business related, and I don't think I'd print any of the images out unless I got really lucky and caught an amazing shot by complete chance.
I'm not opposed to buying a used Canon 70-200L 2.8 IS II, but I don't know if I'll need all of the capabilities this lens offers. This would eat up my entire budget.
I'm leaning towards a used non-IS 70-200L 2.8 and perhaps an 85mm 1.8 & an 18-135 STM for roughly the same price as the 70-200 II. I'd use the 70-200 2.8 for outdoor soccer under the lights, indoor large field soccer and indoor tennis. I'd use the 85 1.8 for indoor soccer on the smaller fields, futsal, and indoor track. The 18-135 would become my everyday lens.