It is not an offence in itself to be in an offside position.
A player is in an offside position if:

" he is nearer to his opponents goal line than both the ball and the second last opponent
A player is not in an offside position if:
" he is in his own half of the field of play
or
" he is level with the second last opponent
or
" he is level with the last two opponents
Offence
A player in an offside position is only penalised if, at the moment the ball touches or is played by one of his team, he is, in the opinion of the referee, involved in active play by:
" interfering with play
or
" interfering with an opponent
or
" gaining an advantage by being in that position

No offence

There is no offside situation if a player receives the ball directly from:
" a goal kick
or
" a throw-in
or
" a corner kick

Infringements/sanctions

For any offside offence, the referee awards an indirect free-kick to the opposing team to be taken from the place where the infringement occurred.

Qualities and Measurements
The ball is:

spherical
made of leather or other suitable material
of a circumference of not more than 70 cm (28 ins) and not less than 6 8 cm (27 ins)
not more than 450 g (16 oz) in weight and not less than 410 g (14 oz) at the start of the match
of a pressure equal to 0.6 - 1.1 atmosphere (600 - 1100 g/cm2) at sea level (8.5 lbs/sq in 15.6 lbs/sq in)

Replacement of a Defective Ball

If the ball bursts or becomes defective during the course of a match:

the match is stopped
the match is restarted by dropping the replacement ball at the place where the first ball became defective

If the ball bursts or becomes defective whilst not in play at a kick-off, goal kick, corner kick, free kick, penalty kick or throw-in:

the match is restarted accordingly

The ball may not be changed during the match without the authority of the referee.


Ball out of play

The ball is out of play when:

" it has wholly crossed the goal line or touch line whether on the ground or in the air
" play has been stopped by the referee
Ball in play
The ball is in play at all other times, including when:
" it rebounds from a goalpost, crossbar or corner flagpost and remains in the field of play
" it rebounds from either the referee or an assistant referee when they are on the field of play