This is a gorgeous shot. The barista is used some nice advanced Pavoni techniques here. Note that he:
– Pre-warms the shot glass using the steam wand
– Pulls the handle up just under the area where the water fills BEFORE locking in the portafilter handle in gently
– Pushes down the handle in the pre-infusion until it reaches a bit of resistance but raises it again before doing a full pull.

Also notice how much pressure he has to exert while pulling the shot. This is how it is supposed to be. If you are pulling a shot with no resistance, you’ll need to work on a combination of grinding finer and tamping a bit harder.