A spelling of ‘maul’, which is usually defined as ‘a massive hammer’ of any kind (OED). Yorkshire examples indicate that malls could be large or small, and were commonly made of iron as well as of wood.
Meanings suggested in the OED include: a miner’s pick, part of the lathe on which objects were turned, a cylindrical rod or axis round which metal was forged, cast, moulded, or shaped.
This is one of several words used by Yorkshire coal-miners for an obstruction in the vein of coal that was being worked, or for a ‘fault’, either of which could cause serious delays.
The several related meanings of this word date back to 1377 at least, referring to devices which were employed to light candles, lamps, and even cannon; usually a piece of slow-burning cord or other material.