Reaching across tabletop, partygoers spilt gin (10)

'reaching' is the definition.
The answer and definition can be both to do with motion as well as being present participle verbs.
Perhaps you can see an association between them that I don't see?

'across tabletop partygoers spilt gin' is the wordplay.
'across' indicates putting letters inside.
'tabletop' becomes 't' (top of the word 'table').
'partygoers' becomes 'ravers' (I can't explain this - if you can you should give a lot more credence to this answer).
'spilt' indicates anagramming the letters.
't'+'ravers'='travers'
'gin' with letters rearranged gives 'ing'.
'travers' inserted inside 'ing' is 'TRAVERSING'.

Can you help me to learn more?