Definitions for "Nightwatchman"
a batsman who comes in to bat out of order towards the end of a day's play in a multi-day game, in order to 'protect' better batsmen
a lower-order batsman who is deliberately sent in late in the day in order to protect a top-order batsman from being dismissed before the end of play
an expendable player sent in late in the day to protect the specialist batsmen from fading light and prowling bowlers