Tamron 17-50 f/2.8. non VC. VC not required for basketball shooting normally, but there are several stabilized med zooms available including stabilized version of above, plus offerings from Sigma & Canon, all in the same F/range.
There are old pilots, & there are bold pilots, but there are no old bold pilots.
What would be a good lens for basketball in a low light gym when sitting left or right of the base line?
Basically you'd need shutter speed around 1/250 to control motion since basketball is a fast paced game, and in a low lit arena that would be difficult if you can't raise ISO high enough to a noise free level so you'll need a very wide aperture.
You'd need something f/2 or faster (which translates to primes) unless you have a newer high ISO body like a 1DX or 5DIII, then maybe f/2.8 would be enough and you could look at zooms like the 70-200. Now if you don't care much about action down court perhaps a 50f/1.4 or 85f/1.8 would work well near the baseline.........
An 85 f/1.8 works great when shooting near the basket--especially if the light is cruddy. A 50mm is O.K., but a little loose. A 70-200 f/2.8 is nice for floor action.
Oops--just saw that you were shooting with a crop frame camera. A plain old 50mm is a good starting point.
Borrow or rent a 50 1.4 and a 85 1.8 and see what works under the basket. The isolation of the 85 1.8 and or shallow DOF will help or hinder shot wide open depending on how close the subject is. To close the shallow DOF will render images soft in forground and background shot at the f-stop you need for light also on a 7D the 85 1.8 is a 136mm eq. it might be to tight. then the 50 1.4 will do well. If you have a 50 1.8 in your bag try it to get an idea but build quallity might be to light for poss action under basket.
The 85 1.8 is on sale for $359.00 till 12/1/2012 so if it's your lens you might need to move.