This is achievement is easy to get if you only go for this achievement.
Go to Championship
, Xfinity Series
(this also works for Monster Energie Cup Series and Camping World Truck Series)
Car doesn't matter, I chose nr 18 Kyle Busch.
to go to the championship settings.
AI difficulty: Custom 85
Race Lenght: 2%
Championship mode sessions: Race only
Damage: No damage
The rest of the settings doesn't matter.
Just play and win the races in the playoffs and the achievement will popup.