When most teams play a front two, it comprises of a small quick guy (called the Number Ten) and a big guy (called the Number Nine). The convention is that when the team is defending, one of these two stays up ahead (just beating the off-side mark, wherever the opposition defence line is), while the other tracks back in order to help out with the defence. The worldwide convention in this regard is for the Number Nine to stay up front in anticipation of an attack while the Number Ten drops back to defend.
Liverpool, of late, however, have played differently. Their Number Ten (figuratively, since he wears seven on his back) Luis Suarez is the one usually left alone upfront when the team is defending, while the number Nine Andy Carroll tracks back to help out in defence.
The logic of this policy is two-fold. One, an additional big player coming back to defend means greater ability to win defensive headers within the box (think of it in terms of winning rebounds in basketball). Secondly, Liverpool under Dalglish have preferred a pass-the-ball-out-of-defence method rather than clearances. This means that when the offence breaks and a counterattack is to be launched, the ball is more likely to be played along the ground to the forward rather than up in the air. And Suarez is the more likely of the pair of forwards more likely to make use of that.
So what is the concept behind the conventional wisdom of leaving Nine upfront with Ten dropping back into defence? The typical strategy in English football is to clear the ball out of defence rather than passing it out, and the big number nine is well positioned to receive it upfront. The big nines usually also have the ability to ‘hold up’ the ball, to allow his team-mates to join him. The number ten, being quick, is able to quickly join the number nine in attack.
The other factor behind leaving the number nine upfront is that they are usually one-dimensional players, with the only abilities being to win headers and hold up the ball. They are either no good in defence, or have big strikers’ egos that prevents from joining defence effectively. Number tens, on the other hand are more skilled all-round and are more likely to come of use in defence.
In this sense, Carroll is not bad at defence, and more importantly he is young and out of form, which makes it easy for Dalglish to force him to track back while defending. So far, it seems to be working.