A lead of 400, entering the fourth innings of a match, is an impregnable position – virtually. A score that is routinely accrued in the early part of a match, becomes unattainable (almost) for the side batting last.
The trend of diminishing run-scoring returns as matches enter their final phase is one of the known, understood and acted upon patterns of cricket. There’s no mystery to it, not if you get close to the action and see the deterioration in the pitch that makes it less and less reliable for batting on as three or four days of play pass.
According to this list, Middlesex’s score of 405-5 against Somerset today is in the top 70 winning fourth innings totals in first class cricket history. This list spans 120 years, meaning that successful run chases of this size, or greater, occur slightly more than every other year on average. In fact, 13 came from the last decade, showing that their frequency is increasing, probably because the condition of pitches alters less as matches progress making run-scoring less hazardous deeper into a match and faster scoring rates mean that leads of 400 plus are achieved at an earlier point in games.
Nonetheless, they remain rare and noteworthy achievements (albeit Middlesex’s second in two years after scoring 472 against Yorkshire in 2014). And each time they happen, their effect is to make another occurrence both more and less likely. Teams facing a target of more than 400 have recent examples to emulate and may opt for the chase rather than survival. But teams setting targets, who can time when the fourth innings begins, will be a little more cautious, asking more in less time of their opponents. For a team on top after three innings, this maxim is particularly true: losing feels worse than winning feels good.