Pre-occupied with the flight of a pass, the movement of their man and on rushing midfielders, central defenders are often under siege and need their full-backs to give the green light for an ambush.
More after the break
From their position out wide the full-back has to watch along the line, be aware of the winger's threat and know when to make the call to 'step up'.
Upon their command the defence pushes out, forcing the attackers to retreat in order to avoid being offside.
Former Tottenham and Republic of Ireland defender Chris Hughton was bestowed with this responsibility from his left back berth.
In this video he explains the roll of a full-back in playing the offside trap.
Chris Hughton will be appearing at this year’s brmb Grass Roots Football Show at the NEC from the 3-5 June. For more information on the biggest grass roots football event in Europe go to www.grassrootsfootball.co.uk
Hughton: Stop the opposition's passing game
Hughton: Last 5 mins and you need a goal
Winning the ball off the target man
How to make the opposition play the long ball game
Countering a team that press high up the pitch