Add a missing s

rules/game_process.tex

@@ -215,7 +215,7 @@ \subsection{Initial Kick-off}
 % If a team places robots themselves for initial kick-off, it is allowed for the team to vary the spacing and orientation of the robot positions along legal positions on their half's touchlines~(see also~\cref{sec:inside_outside}).
 
 Robots are brought into the \texttt{initial} state after they are placed.
-Once the robots receive the \texttt{ready} visual signal from the referee or the signal from the GameController, whichever happen first, they proceed as described in \cref{sec:kick-off}.
+Once the robots receive the \texttt{ready} visual signal from the referee or the signal from the GameController, whichever happens first, they proceed as described in \cref{sec:kick-off}.
 
 % \begin{figure}[t!]
 %   \begin{center}