The ghosting effect you see is called motion blur. You need to speed up your shutter speed. For Tennis you will need a minimum of 1/640 to avoid too much blur. 1/1000 is better. To achieve such speed you need light. A 7D or 60D will not fix this problem as it is the same for all cameras.
First, dont use the camera in P mode. To control you shutter speed while keeping the rest at automatic, select TV mode and try pushing up the shutter speed. For normal moving human subjects, I always use at least 1/160. For street photography 1/300. If I were to shoot sport, I'll use the highest shutter speed available.
The higher the shutter speed, the higher ISO will jump if you dont have enough light. That mean your pictures will be more noisy. Try and set your ISO to 6400 just to see. I've set ISO 3200 to be the maximum in the menus of my cam.
For night sport like on your pictures, you will need a really fast lens (f1.8 or f1.4) and high ISO speed. Probably 3200 or even 6400. You can apply noise reduction afterward inside your favorite editing software.
http://thediscerningphotographer.com …ter-speed-in-your-photos/
If you want to do casual low light, I'd recommand getting the ef50mm f1/8 lens. for 100$. For night sport on a budget, I'll look at the ef85mm f1.8 as it is one of the fastest focussing lens canon make. (the 50mm is slow to focus)
If you want the flexibility of a f2.8 zoom on a budget, I think your best bet is the Tamron 28-75mm f2.8. You can find it for 300$. Not super fast to focus but the focal range is good and the image quality is great while being a f2.8 lens.
good luck!