A pull off is not quite the opposite of a hammer-on,
however the concept is similar. Similar to a hammer-on the goal is to make another sound with picking the string. To
execute a pull off your fret hand presses down and pulls down on the string but does not bend it but instead 'plucks' it.
Let's break it down:
You will be pressing down on both the 9th fret and 7th fret
You will pick the 1st string
You pull down your 3rd finger until it pulls off the string; essentially your third finger ends up plucking the string.
This will cause the 7th fret to be heard.
Remember all of this done with just one pick of the string.
Play a pull off:
1. Place your 3rd finger on the 9th fret of the 1st sting.
2. Place your 1st finger on the 7th fret of the 1st sting.
3. Pick the 1st string.
4. Pull your 3rd finger down (not bending the string) so that it plays the 1st string again.
5. Your 3rd finger should be lifted up and the 5th fret note should now be playing.