When cask beer aka ‘naturally conditioned’ beer was first delivered the standard practice was to let it settle for a day or so before ‘tapping’ it, I.e. opening the cask by tapping in a soft spile, usually made of cane. This let some, but not all of the CO2 caused by natural secondary fermentation in the cask escape without bacterial ingress from the atmosphere. Most breweries in England ‘primed’ their product with sucrose to nourish the yeast and encourage this, it raised the alcohol content slightly and gave the beer a natural “fizz”. In warmer weather in the days before temperature controlled cellars with a/c this often made the beer quite fizzy initially and this was called ‘new’ ale or ‘green beer’. Drinkable, but a bit sweeter, more effervescent and often slightly hazy from the yeast particles.
Draught Bass was particularly prone to this but many of the (mostly extinct now) regional bitters of England exhibited it.
There you go, ‘new’ ale…