Here is an interesting link about boxing stances. Note how the pic matches the stance on the fob...
I haven't been able to find it, but I would guess from the detail (the boxer's stances, the faces, the ropes, even the carnival tent roof lines) that this fob was based on a drawing or photograph of an actual fight that took place, possibly a souvenir of the event. Lots of links to the history of boxing, with some pics of Dempsey looking close to the correct era of the figure on the left. If you can find the drawing/photograph, you'll be a long way towards ID'ing and dating this neat find.
From the link below:
Now, moving onto the bareknuckle stance that most people are familar with from boxings Golden Age, John L Sullivan, Paddy Ryan, Jem Mace, Heenen, Sayers....etc. Fig 2 and 3 show this strange extended lead stance with the arms held relatively low and the legs very straight. It is very different from the modern stance we are so used to seeing. Does this mean it was not as effective as the modern stance? No, it just means that boxing had different rules, and like the modern stance, the older stance catered to the rules of the game. These rules were known as the London Prize Ring Rules, or, to save myself the trouble, the LPR. The LPR took over from the Broughton rules in 1838. They were very similar but slightly more refined than the earlier system. Let's take a quick look at what was deemed illegal under the LPR....<<<