Small beers, gas and pitch (5)
I believe the answer is:
sales
'pitch' is the definition.
('sales pitch' can be a synonym of 'pitch')
'small beers' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'beers' becomes 'ales' (I've seen this before).
's'+'ales'='SALES'
'gas and' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for sales that I've seen before include "Occasions for buying at reduced prices" , "Periods of price reductions" , "Opportunities to sell" , "a feature of Boxing Day?" , "Cheap offer periods" .)