How can I detect if a person takes fall damage?
Solution 1:
Create two scoreboard objectives like following:
/scoreboard objectives add fall stat.fallOneCm
And:
/scoreboard objectives add damage stat.damageTaken
Then on a fill clock run:
/effect @a[score_fall_min=1, score_damage_min=1] EFFECT_HERE
/scoreboard players reset @a fall
/scoreboard players reset @a damage
How this works is that it effects all players with a fall distance statistic score of the minimum 1 which also has a damage taken statistic score of the minimum 1. After that it resets the scores so that it can happen again.