Never realized this until the credits in Racing the Rain.
https://www.celticsblog.com/2010/4/21/1434104/allen-celtics-run-heat-out-of-town
Ray Allen joined his mother, Flo, for the final two miles of the Boston Marathon yesterday. Allen, who prides himself in staying in the best possible shape he can be in, was sitting at his locker tonight with the book, "Once a Runner" by John L. Parker by his side. The book, regarded by many as one of the best books on running ever published, illustrates how much work goes into being a truly great runner. Much like some of the best runners in the world, Allen has spent the majority of his life training to be the best at his sport, basketball. Asked whether he would someday run the Boston Marathon, Allen smiled and said, "As soon as I retire."