For #2 Player goal count can be done by mapReduce, map games to playerid,goals en then sum the goals.
Elo history #40 is redudant data for creating graphs, you can always recalculated the history with the games.
a goal object would be nice (stored as a list of goals in Game), so we can see when you scored, crawl data, and later add flags for own-goal, '5'-goal, etc.
With code like
the logic behind scoring and winning a game in progress is not up to par. Revision is needed.