Cap on the old man in American city (5)
I believe the answer is:
Here is my best explanation:
'american city' is the definition.
'cap on the old man' is the subsidiary indication.
'cap' becomes 'tam' (tam is a kind of cap).
'on' means one lot of letters go next to another.
'the old man' becomes 'pa' ('pa' can be a synonym of 'old man').
'in' is the link.
(Other definitions for tampa that I've seen before include "Port of western Florida", "Florida resort", "American resort", "US town", "US resort", "stateside destination", "City in Florida", "American city", "US city" and "Floridian resort".)