Could you please tell me if sprinting on my off days will effect my strenth training. I need to build endurance for rugby, which will consist of lots of running like soccer, but at the same time I need to build strenth and power.

You won't be able to gain strength as quickly if you are doing large amounts of running. But, if you are an athlete it comes with the territory. You have to run, and, you have to be strong. The key with surviving and ultimately succeeding with this type of schedule is to make sure your recovery levels are at their peak. You need to be sleeping 8-10 hours every night. You must eat nutritious meals 4-6 times per day. Supplements will help to maximize your recovery ability as well as increase your performance in strength and muscular endurance! If you give your body the fuel in needs for high performance you will reach your goals.