UPDATE P
    SET P.Inactivity = P.Inactivity + 50,
        P.Processed = 1
    FROM dbo.Players as P
    LEFT JOIN ( SELECT PlayerID
                FROM dbo.PlayerToWar
                WHERE WarID = @WarID
                ) X
    ON P.PlayerID = X.PlayerID
    WHERE P.PlayerID = NULL and P.Processed = 0