Client

ShouldSit (Player ply)

return true to disable needing walk to sit

Server

OnPlayerSit (Player ply, Vector pos, Angle ang, Entity parent, Number parentbone, Entity vehicle)

Called whenever a player sits down return false to cancel sit

OnGroundSit (Player ply, Table EyeTrace)

Called whenever a player sits down return false to cancel ground sit

CheckValidSit (Player ply, Table EyeTrace)

Checks if a sit is valid before sitting, takes priority over ConVars.

Return value	Effect
true	The seat position is valid
false	The seat position isn't valid
none	Default behavior

ShouldAllowSit (Player ply)

Return false to disable sitting for a player, takes priority over admin only convar.

Return value	Effect
true	Allows sit even when not admin
false	Denies sitting under any circumstance
none	Default behavior

HandleSit (Player ply, Table dist_profile, TraceResult eyeTrace)

Bit of an internal function that allows you to define your own behavior for when someone presses ALT+E (look at ground_sit for an example)

Return value	Return value 2	Effect
true	Vehicle veh	Stop sit processing and return vehicle if created
any	any	Continue sit processing