Observe, taking in bridge team’s rational approach (5)
I believe the answer is:
sense
'rational approach' is the definition.
(sensible approach)
'observe taking in bridge team's' is the wordplay.
'observe' becomes 'see' (observe can mean to see something).
'taking in' indicates putting letters inside.
'bridge team' becomes 'NS' (north and south are a team in bridge).
'see' enclosing 'ns' is 'SENSE'.
(Other definitions for sense that I've seen before include "Sat lazily; hung loosely" , "A particular meaning" , "Become aware of" , "Tenor" , "Feeling - reason" .)