Taking photos in gyms is a challenge because the light is rarely good. Not only is there a lack of quantity of light, but the quality of light is awful too. Setting a custom white balance would be a good idea. But I usually just use auto white balance and correct in photoshop. Clearly, not the best method. I'm going to try to remember to bring that grey card to the games next year!
I use my 85mm 1.8 lens for basketball. Since I have a full frame camera, the 50mm would be very close to this focal length on a crop sensor camera. If you have a 50mm with a wide maximum aperture of either 1.4 or 1.8, that would be a good choice. I keep the auto focus point in the center. I don't have time for creative composition or focus and recompose so I just follow the ball and frame the shots so that the player with the ball is in the center. I shoot in ai servo mode which follows movement for focus. I do have the drive set to continuous, but I try to just take one shot at a time at the right moment... just because I don't want a ton of shots to have to upload. :)
With the 85mm I have to crop in camera a little sometimes, but I'd rather do that than use a zoom with a 2.8 maximum aperture. That would require an even higher iso.
I shoot in aperture priority mode. I set my aperture as wide as it will go and then I set my iso to the lowest setting possible that will still give me a shutter speed of at least 1/200. A faster shutter speed would be better, but the gym I shoot in is pretty dark so I'm already at iso 2000 and I don't like to go much higher unless I have to.
I stand near the corner of the court and I shoot mostly vertical shots. My favorite shots are those that include the player, the ball and the goal.
I sometimes shoot horizontally if I decide to shoot the action at the opposite side of the court. Oh and my other favorite shots are the ones that include Mason! He didn't get too much playing time this year, but I was very proud of him for getting asked to play up on the high school team as an 8th grader. He loved it.
I'm no expert at sports photography, but this is how I do it. Maybe there are ways to get better results? I will keep studying and practicing and of course I'll share if I figure out a better way!