Share 'How to track league player improvements?'

Our new league stats ina couple of weeks and I have an idea to award a trophy to the player who improves most throughout the 10 week league period.  I know I can look at a players average and determine it from that  but how do I get a starting number?  Someone give me a hand with this so that i can discourage baggers.  I was thinking about recording the first 2 or 3 scores, taking the average, th…