Thanks, Bobby. Have another look at the rows with the oddly entered answers. Each one of those has an anagram of a particular 'activity', and also an anagram of a synonym for ... lunacy, say. The versions (of the activity) at 1 A , 33 Aand 41 A were my way in, I confirmed some others later.
If you've got the activity, there's a really useful word to be seen right across the grid. I needed Google/Wiki to find the 'reason' - that came only after I'd finished the name from the Down letters.