I am not all that sure on how the balls will be scored but in the shematics it did not show of any thing so im am guessing that they might use a light sensor in the back of the holding box for both the side and center goals, but if I were you i would go
www.usfirst.com and send them an e-mail asking how they would be scored they most likly will answer back but there is not a 100% chance, but it is worth a try. Sorry, this is not related, but you should try out Runescape if you have not already its really good.