First dirty mat takes athlete to be a smuggler (4-6)

'be a smuggler' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'first dirty mat takes athlete' is the wordplay.
'first dirty' becomes 'd' (rst letter of 'dirty').
'mat' becomes 'rug' (I've seen this before).
'takes' means one lot of letters go next to another.
'athlete' becomes 'runner' (runner is a kind of athlete).
'd'+'rug'+'runner'='DRUG-RUNNER'

'to' is the link.

Can you help me to learn more?