Positions

There are no fixed positions (even a goalkeeper is not required under the 2007 rules), but most teams arrange themselves (in a similar way to Association football teams) into fullbacks (defence), midfielders (halfback) and forwards (front line). Many teams include a single sweeper. The rules do not specify a minimum number of players for a match to take place, but most competitions have some local ruling on this, with seven players being a common minimum.
One player from each team may be designated the goalkeeper. Goalkeepers must wear a suitable helmet with full face mask and are also permitted to wear protective padding, including large leg guards, kickers and gloves. Although goalkeepers may block or deflect the ball with any part of their bodies, and propel the ball with their feet (and from 2007 any other part of their equipment in a "goal-saving action"), they must always carry a stick. The goalkeeper is permitted to play the ball with his stick at above the height of the shoulder when in her/his own defensive circle. Goalkeepers are permitted to play the ball outside their defensive circle (scoring area or "D"), but may only use their hockey-stick in this circumstance, not their kickers; leg-guards; gloves/hand protectors or any part of the body. Fully protected goalkeepers are prohibited from passing their side's defensive 23 m line during play, unless they are taking a penalty stroke.

Credited to Wikipedia