Hi first of all what is your budget for a new lens "break the bank" means different things for different people. I'll get my colleague Rodger to further assist he's a sports photographer. For sports usually a telephoto lens with a wide aperture is needed. Gyms are often very dim. You or the camera will have to push the ISO up very high such as ISO 3200 or 6400. What sport is it basketball or a different sport.
-Demetrius
Bodies: EOS 5D Mark IV
Lenses: EF Trinity, EF 85mm F/1.8 USM
Retired Gear: EOS 40D, EF 50mm F/1.8 STM & EF 70-210mm F/4
Speedlites: 420EX, 470EX-AI, 550EX & 600EX II-RT
