In the sport or as some may say art of basketball it is commonly known as a dunk. "Yammed" = past participle.
To get more in depth with the term, it would be used to describe an EMPHATIC DUNK!
1. The kind of dunk to make you lean back in surprise and say "DAMN!"
2. The kind of dunk where it was so NASTY that it made everyone in the immediate observable vicinity go wild due to the amount of hype a player gets for dunking on another emphatically.
3. The kind of dunk in which others may think, "How the hell did Mike do that? He's only 5'4 but he dunked on the 7 footer!" It wasn't a hard dunk, but the fact that they pulled it off is reason enough to give props. (If you use your brain, you'll get it.)
4. The kind of dunk that rattles the rim, the backboard and the stanchion so much that it looks like a hurricane just hit it.
Ex 1. Did you see that one dude yam that thing from the free throw?
Ex 2. When Carmelo Anthony caught the steal and then went straight to the rim off a drop step and yammed it in Paul Milsap's face during the '09-'10 season.
Ex 3. Spud Webb and his yam on Manute Bol.
Ex 4. When Dominique Wilkins yammed the goal on any occasion period