zlacker

A diversion - something that is separate from the main activity, something done for amusement's sake.

The field - outdoors, countryside, perhaps an actual field, though not necessarily.

>>taylor+(OP)
I think in this context "the field" means in the sense similar to "the field of study", i.e. the encompassing boundaries of an endeavour. So in this case long distance canoeing is an off the beaten track distraction from the sport of canoeing (or in the contrapositive, an off the beaten track distraction from long distance travel). The phrase is enticing because it could be interpreted either way; and still have largely the same meaning.

>>tanken+E4
I was thinking in the context of "field sports", such as hunting shooting etc.

As you say though, both are plausible, and that ambiguity is part of what makes the phrase so interesting.

>>tanken+E4
In this sense any diversion would have a "field" so saying "diversion of the field" would be redundant. As a definition of sport, it is much more likely that "field" means the outdoors (there probably were not many indoor sports at that time).

However, this shows why this dictionary is not actually good for modern, practical use, IMO.