Can I use grok to match fields?

Elastic Stack Logstash
1

Is it possible to use grok to match multiple fields using regex?

I have the metrics filter generating logs. Fields are generated per host and look like event.$HOST.count

At this point I'm trying

match => [ "event\.%{DATA}\.count", "0" ]
add_tag => "inactive"

Configtest shows no errors, however I cannot see anything generated here. Totally understand if this isn't possible.

2 
match => [ "event\.%{DATA}\.count", "0" ]
add_tag => "inactive"

Is this snippet from the grok filter? What is it supposed to mean? The match parameter of a grok filter should point to an array (or hash, I suppose) where the first element (or hash key) is a field name to match against and the second value (or hash value) is the grok expression. So,

match => ["message", "event\.%{DATA}\.count"]

makes sense (although nothing it captured) but what you have above doesn't.