In 1963, Plimpton attended preseason training with the Detroit Lions of the National Football League as a backup quarterback, and he ran a few plays in an intrasquad scrimmage. These events were recalled in his best-known book "Paper Lion", which was later adapted into a 1968 feature film starring Alan Alda. Plimpton revisited pro football in 1971, this time joining the Baltimore Colts and seeing action in an exhibition game against his previous team, the Lions. These experiences served as the basis of another football book, "Mad Ducks and Bears", although much of the book dealt with the off-field escapades and observations of football friends Alex Karras ("Mad Duck") and John Gordy ("Bear"). Another sports book, "Open Net", saw him train as an ice hockey goalie with the Boston Bruins, even playing part of a National Hockey League preseason game.