Complex sentence: Super Bowl LI was the Patriots' record-setting ninth Super Bowl appearances, their second in three years, and their seventh under the leadership of head coach Bill Belichick and quarterback Tom Brady.
Split into simpler sentences: Super Bowl LI is the Patriots' ninth Super Bowl appearance, the most Super Bowl appearances of any team. It is also their second appearance in three years and their seventh under the leadership of head coach Bill Belichick and quarterback Tom Brady.