All protective equipment must be approved by the umpires to ensure that it can not injure other players. The game is played with an ellipsoid ball, on a grassed oval. Four posts, aligned in a straight line, apart from each other ( in total length), are erected at either end of the oval. The size of the ground is not fixed, but is generally between long and wide. Lines are drawn on the field to mark   The game is a fast-paced combination of speed, athleticism, skill and physical toughness. Players are allowed to tackle the player with the ball and impede opposition players from tackling their teammates (known as "shepherding"), but not to deliberately strike an opponent (though pushing the margins of these rules is often a substantial part of the game). Like most team sports, tactics are based around trying to get the ball, then – through a combination of running with the ball, hand-passing (punching the ball from the open palm of the other hand) and kicking – to deliver it to a player who is within range of goal. Because taking a mark entitles the player to a free kick, a common tactic is to attempt to kick the ball "on the full" (without bouncing) to a teammate who is within kicking range of goal. In this situation, packs of players often form around the goal square, and the opportunity arises for spectacular marks in which players launch themselves off opponents' backs to mark the ball, high in the air. This particular skill is highly regarded as a spectacle, and an annual "Mark of the Year" is awarded at the end of a season. There are no set positions in the rules of the game, but traditionally the field was divided into three major sections: the forward line, back line, and midfield. The forward and back lines consisted of six players, arranged into two lines of three players each. The midfield generally consists of the designated "ruckman" (i.e. player who contests the "ruck" or "bounce-down") and players who either stay in the centre area of the ground (between the two 50-metre arcs) or follow the ball and are not confined to a particular area. The modern game, however, has largely discarded positional play in favour of a free flowing running game and attempting to have loose men in various positions on the ground. The rise in popularity of the hand-pass since the 1970s has greatly influenced this style of play, with players more willing to follow the ball and move it quickly amongst themselves rather than kicking long to a one-on-one marking contest.