I'm sorry that this is very late but I've just finished (I hope) this crossword and am unable to parse 17a.
Underrated beginner in ultimate card game babbled holding diamonds back. (13)
U_A_P_E_I_T_D
I have unappreciated (def. of underrated)
U (beginner in ultimate)
nap (cardgame)
I'm afraid that I'm struggling with the rest.