After which a bat may be aloft, not upside-down (3)
I believe the answer is:
ton
'after which a bat may be aloft' is the definition.
I can't judge whether this definition defines the answer.
'not upside-down' is the wordplay.
'upside down' shows that the letters should be reversed in order.
'not' reversed gives 'TON'.
Can you help me to learn more?
(Other definitions for ton that I've seen before include "2,240 lbs" , "A slangy 100 mph - heavy" , "A slang 100 mph" , "Two thousand, two hundred and forty lbs avoirdupois" , "Heavy weight or 100mph" .)