Think of your body as a "kinetic chain." The movement of your arms and legs actually begins with the spine, and that's why a strong core will help you in any sport.
If you want to take your sports performance to the next level, you'll make time for core workouts. For example, if you're a runner with strong legs, that's great. But if you ignore your core, the weak muscles in your hips and low back won't give your legs the support they need to carry you through longer or faster runs. Similarly, if you are a golfer, a stronger core body improves the stability to your arms and legs as you extend through the full range of motion in a golf swing.
The "bridge" is an easy core exercise that you can incorporate in to your pre-practice or competition warm-up.
Here's how to do it: Start by lying on your back with your knees bent and your feet flat on the floor. Don't press your back into the floor, but don't arch it. Keeping your back in this neutral position, lift your hips off the floor and engage your abdominal muscles. Lift your hips high enough to line up with your knees and shoulders, but remember to use your abs, not your glut muscles, to hold your hips high. Keep your arms alongside your torso, but avoid using your arms to raise your hips up. Take 3-4 deep breaths and release to the starting position. Be sure to keep your feet parallel to each other to avoid any strain on your knees.