Folly of new and old bridge partners seen playing (8)
I believe the answer is:
nonsense
'folly' is the definition.
(I've seen this before)
'new and old bridge partners seen playing' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'and' says to put letters next to each other.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'bridge partners' becomes 'ns' (I've seen this in other clues).
'playing' is an anagram indicator.
'seen' with letters rearranged gives 'ense'.
'n'+'o'+'ns'+'ense'='NONSENSE'
'of' is the link.
(Other definitions for nonsense that I've seen before include "Bilge, drivel" , "silly ideas" , "double Dutch?" , "Cobblers" , "Codswallop, hooey" .)