Bruce Moore (a former director of the Australian National Dictionary Centre, currently editing the second edition of the Australian National Dictionary) discusses the meanings and history of the Australian slang verb dob in an extract from his book What’s their Story? A History of Australian Words (Oxford University Press Australia, 2010), quoted in this Ozwords post:
The verb dob has a range of meanings in Australian English. The most common meaning (often in the form dob in, dob into, or dob on) is ‘to inform upon, to incriminate’ … It can also (and less commonly) mean ‘to impose a responsibility upon (often a matter of getting someone to do an unpopular or difficult task)’ … As dob in it can also mean ‘to contribute money to a common cause’ … Finally, in Australian Rules football, dob can mean ‘to kick (the ball) long and accurately; to kick (a goal)’ … Are all these meanings related?
A possible clue to the origin of this major sense of dob, and also the other dobs, may lie in British dialect. … In fact, most dictionaries trace the Australian dobs back to these British dialect dobs. There, we find the verb dob meaning ‘to put down an article heavily or clumsily; to throw down’, with widespread dialectal usage… A second dialectal meaning of dob is ‘to throw stones etc. at a mark’, mainly from northern English dialects, and from Cornwall. … In Lincolnshire dob means ‘to hit’ or ‘a hit’. The underlying notion of throwing and hitting is evident in some marble games. In Cheshire the verb dob means ‘to throw a piece of slate, or other flat missile, at marbles placed in a ring at a distance of about six or seven feet from the player’, and in Northamptonshire ‘When one boy strikes another boy’s marble, without his marble first touching the ground, he is said to dob on it’. A dobber in British dialect is ‘a large, heavy marble’ and a dob-taw is ‘a large marble, a “lobber”’. In most of these uses the dialect dob is synonymous with the more familiar dab, and with some of that word’s dialectal uses—for example, a dab can be ‘an amount of money’, and to dab down means ‘to put a thing down quickly’ and figuratively ‘to pay down ready money’.
This is clearly a very complex etymology. The problem with what is outlined here is that those Australian words and meanings, which we are certain have their origin in British dialect, appear during the second half of the nineteenth century, when the influence of dialectal words on Australian English was at its greatest. The Australian dob and its variants are first recorded much later then this. … On these grounds we must conclude that the origin remains uncertain, although the clues provided in the dialectal material certainly provide some very likely origins.
An admirable example of how the nitty-gritty of etymology is carried on; see the link for citations, references, and further speculation.