You're conceptualising it incorrectly. It's not an opposed roll where only one can succeed, it's a serious of fictional moves. So.
Fighter decides he's had enough of the Bard's lip and attacks him. Hack and Slash.
Bard tries to leap aside. Interfere.
I'd roll the interfere first: roll+Bond, strength is irrelevant, using your numbers the bard gets a 10, so he succeeds in making it difficult for the fighter to hit him. So he anticipates the blow because he know the Fighter is a sociopath with a mean temper, or he starts crying and the fight has to force himself to hack down his friend.
Now the fighter rolls his attack: roll+STR, minus two for the anticipation or crying or whatever, 7+2-2=7, so he hits and does damage, but the Bard gets to make an attack.
Note that you could also have the fighter roll hack and slash first ("A 10! His longsword carves through the air. It's coming right at your head, what do you do?!" "I duck!", then the bard rolls interfere ("An 8! You duck your head under his blade, but the sharp movement causes you to lose your footing, you fall over!. Fighter, 10-2 is 8, you mange to adjust your strike, but doing so pulls you off balance and opening you up to the Bard's counter attack...")
For me, the Fighter's hack and slash 7-9 is the slightly problematic bit. What happens here? Does the Bard inflict his damage on the fighter? does he get an attack on the fighter? Something else?
I think, as the GM, I would ask the bard what they want to do. If the Bard has had enough of the Fighter's bullying and stabs him with his dagger, I'd probably just let him inflict damage (hey, don't start fights if you can't take the counterattack!), but allowing an interference-free hack and slash might be more in the theme of "moves snowballing".
What would other people do?