Is chock-a-block with people playing games, we're told (5)
I believe the answer is:
teems
'is' is the definition.
The definition and answer can be both to do with fundamental existence as well as being verbs in their -s form.
Perhaps there's a link between them I don't understand?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for teems that I've seen before include "Rains heavily" , "Abounds, swarms" , "Pours down" , "Buckets down" .)