Soccer Scoop. Who's making a fool of Mac?

Mac is the best goalie on his soccer team -- and he's not afraid to let everyone know it. Then somebody on the school newspaper creates a new comic strip that caricatures Mac and his performance on and off the field. Mac wants to put a stop to it, but no one seems to know who the cartoonist is. He thinks it must be someone on the soccer team itself, because the strip is too tightly connected to the team for it to be an outsider.
But his suspicions lead to one dead end after another. Can he discover who the artist is before the comic strip gets out of hand?