Leg Strap is an accessory that comes with Ring Fit Adventure along with the Ring-Con. It is required to play the game. The Leg Strap is a strap made from elastic and Velcro which sits around the left thigh when in use. It contains a pocket which the left Joy-Con can be placed into. It is also used to track the player's movement. The strap will also be used for Nintendo Switch Sports in 2022.
Ring Fit Adventure Wiki
Leg Strap, Ring Fit Adventure Wiki
Leg Strap, Ring Fit Adventure Wiki
Wii Fit - Wikipedia
Adventure Mode, Ring Fit Adventure Wiki
Ring Fit Adventure Guide - IGN
Ring Fit Adventure Guide - IGN
JoJo's Bizarre Adventure: Stone Ocean - JoJo's Bizarre
Leg Strap for Nintendo Switch Ring Fit Adventure and
Jean Pierre Polnareff - JoJo's Bizarre Encyclopedia