Upstater may have influenced me into thinking something was wrong with the sentence, and I read it with some bias, but (leaving aside the began/begun issues) if the brain processes that he had "already begun to attend Findlay" since those words run together, the rest of the sentence falls apart. It took me a second read to decipher what I thought was jibberish the first time.
"To attend Findlay" explains why he left Australia, so it is better sentence structure to keep those portions of the sentence together and then add the additional information about the when ("after his senior season had begun") at the end. Of course, Goodman was a bit unlucky. The same clause that reads, for example that he "left Australia after Christmas to attend Findlay" is perfectly clear. But he "left Australia after Fishy was sentenced to attend Findlay" is not. Was Fishy sentenced to attend Findlay? Or was he sentenced to prison and that is just a point of reference for the timing of when the subject went to Findlay?
It could very well be that Goodman has been dead on accurate about everything as a columnist, but sentence structure has held him back. For example, when he wrote that Daniel Hamilton is a selfish gunner who will only pass the ball if you put a knife to his throat, he may have actually meant that he's a versatile wing who can beat you in any number of ways, but he didn't use the Oxford comma.