A few points:

You've apparently got the same name ("ChallengesTheStrong") for both your trait and your trigger. I can't say this is definitely going to cause a problem, but you'll notice that this is never done anywhere else in export_descr_character_traits.txt.

In order for the BattleOdds condition to recognize its parameter as a number, it needs to begin with a digit; you want "0.7" rather than ".7".

Note that there is already a trait somthing like this: "GoodRiskyAttacker".