Substitutes in Rugby Union can be used in a variety of different ways. Cover for injury was the original reason for substitutes and is still the primary consideration.
Alternatively, substitutes can be used as "impact players" to change the course of events, or to help prevent injuries. Additionally, sometimes substitutes are used to give players experience before risking them in a starting role.
This latter use of substitutes can be flawed and for it to work the matter needs to be handled correctly. In the current England side, the majority of the starting XV are experienced and trusted players.
By contrast, Martin Johnson has mainly selected his bench from talented players, who are raw and evidently not trusted for the starting roles.
During England's most recent games in Cardiff and Dublin, Johnson has left his substitutions until very late in the game. With the talent of Care, Tait, Croft and Hartley coming onto the field, it has been no surprise this has coincided with England's best attacking spells.
However, it is equally no surprise that this has also been England's worst period for avoidable penalties and sin-bins.
To understand this phenomenon in more detail, it is worth considering the mind-set of the young English substitutes. Under the recent EPS agreement, they have been taken away from their club environment, where they are regularly in the first XV.
They have to go through rigorous training for two weeks before an international, dreaming of playing for England.
Their only release from all the hype and pent up emotion is the actual game. For members of the starting XV this emotion can be let out in the early part of the game and helps to get them through 80 minutes.
For the young bench player, they release two weeks of emotion into sometimes as little as five minutes of action. With this in mind, it is no surprise to see over-eagerness and too much aggression.
Shane Geraghty and Danny Care have both recently been sent to the sin-bin in the last 15 minutes of recent England games. Both of these players are under 23 years of age, have started games for England in the past, but have recently had to spend time on the sidelines watching other players strut their stuff on the big stage.
They are both desperate to show they should be in the run-on side. Yet, they are given such a short period of time to impress. The result has been an uncontrolled performance, where they give away far too many penalties and yellow cards.
How substitutes are being used is currently costing England test matches. Martin Johnson needs to give the substitutes more game time to make a difference or needs to instill a greater sense of calm from those who come on at the end of games.
Of course, he could change tact, become more adventurous and pick these talented youngsters from the start!