Bill in club, upset (3)
I believe the answer is:
Here is my best explanation:
'bill' is the definition.
(tab is a kind of bill)
'club upset' is the subsidiary indication.
'club' becomes 'bat' (bat is a kind of club).
'upset' is a reversal indicator.
'bat' backwards is 'tab'.
'in' is the link.
(Other definitions for tab that I've seen before include "Tally of orders in bar", "Label", "Text indent key", "Kind of label for bat", "Small flap - bill", "Bar tally; small flap", "Bill", "Flap; meal bill", "The bill in a restaurant" and "Tally at bar (colloq.)".)