An "A" is the highest grade in the US grading system, so when it says the girl's legs were an A, it just means they were nice and he would have given them the highest grade. "I made my winning move" is saying the person took an action that either impressed Jenny, or got the person something from Jenny, like a kiss or something. If "The crowd were screaming for blood or a goal" it means that the crowd was going crazy, they were probably very excited about the game and wanted to either see a goal made or see someone get hurt.