The SR button refers to the right shoulder button on the Joy-Con, when it is detached from the Nintendo Switch. The wrist strap that comes with the Joy-Con can be attached to make the button easier to press. When using dual Joy-Cons, it serves no purpose. When using a single Joy-Con, it serves as an equivalent to the R button, acting as a shoulder trigger. In Ultimate, it is used for shielding attacks, much like how the R button is solely used for shielding in Super Smash Bros. for Nintendo 3DS. It and the SL button are present on both the left and right Joy-Con controllers.
|Controllers and buttons|
|Nintendo 64 controller|
|Wii Remote (and Nunchuk)|
|Wii U GamePad / Pro Controller||LR|
|Switch Pro Controller||LR|
|Third-party controllers||Hori Mini Pad · Arcade controller · Keyboard|