To fumble is an action that displays a lack of finesse or grace...
So what you're looking for in this analogy is a word that describes what maligning someone shows a lack of.
To solve this, you'll need to understand the definition of "malign":
So ask yourself: "What does someone who speaks ill of other show a lack of?"Malign - speak about (someone) in a spitefully critical manner.
"don't you dare malign her in my presence"
There are a number of options here:
Respect
Niceness
Civility
Kindness
These are just a few examples.
If this is an SAT question, then you'll have multiple choice options to choose from, so take a look at them and work out which ones matches most closely!