Are you shooting at night? Are you shooting with a fast lens? What does your shutter speed look like?
To quote Bryan Petersons Understanding Exposure:
When you want to freeze any moving subject, you need to consider three factors: The distance between you and the subject, the direction in which the subject is moving and your lens choice. First determine how far you are from the action. Ten feet? One hundred feet? The closer you are to the action, the faster the shutter speed must be. Next determine if the action is moving toward or away from you. Then decide which lens is the most appropriate one.
For example, if you were photographing a bronco rider at a distance of ten to twenty feet with a wide angle lens, you have to use a shutter speed of 1/500 sec. to freeze the action. If you were at a distance of one hundred feet with a wide angle or normal lens, his size and motion would diminish considerably, so a shutter speed of 1/125 sec. would be sufficient. If you were at a distance of fifty feet with a 200mm telephoto lens, 1/500 sec. would be necessary (just as if you were ten feet from the action). Finally, you'd need a shutter speed of 1/1000 sec. if the bronco rider were moving parallel to you and filled the frame either through your lens or your ability to physically close.
I wonder how many questions here I could answer with a direct quote from this book?
Not to be rude. Sorry. Basically, you need to keep your shutter speed up. Anywhere from 1/250 to 1/1600. Shutter priority (S on nikons don't know on canons) mode will help with this. If you're shooting at night, or really any time with poor light, good luck.