John Leonard Sadler (born 19 November 1981) is an English cricketer and cricket coach. He is the head coach of Northamptonshire who succeeded David Ripley following the 2021 season. As a player, Sadler played county cricket for Yorkshire, Leicestershire and , and also represented the Yorkshire Cricket Board. After a spell on the Leicestershire coaching staff, he joined Northamptonshire for the 2020 season. He succeeded David Ripley as head coach in September 2021. Sadler has cited former Leicestershire batsman Tom New as his idol.