The former couple stood on the sidelines together -- apparently on friendly terms -- while their 8-year-old son played. Son Sean Preston was also on hand to root for his brother.
Spears and Federline were married for two years and divorced in 2006.
Federline's ex-volleyball player wife, Victoria Prince and their 2-year-old daughter Jordan, were not on hand for the game. Neither was Spears' live-in boyfriend, law firm field researcher David Lucado.
Megyn Kelly: Santa Claus and Jesus are both white men
Wisconsin business offering 'therapeutic cuddling' forced to close