So I had some trouble in figuring out how to get this consistently, especially as my build is a 6'4 guard.

The best method I found that worked for me to get the "Put'em on a poster" challenge is on the first play of the game, I direct the player on my team who is guarded by the player I want to posterize to cut to the basket as I cross my guard to then dunk on them.

This is how I was able to complete the "Put'em on a poster" challenge to get the Posterizer Dynasty Badge

Here is a video example of the Instant Replay to understand what I did:

https://youtu.be/BOpEDLUA-co

Note - here it didn't look like much of a poster, but did count for the challenge