Doctor Who hands over Rose finally -- big mistake (6)
I believe the answer is:
howler
'big mistake' is the definition.
'howler' can be an answer for 'mistake' (I have seen 'Serious mistake' mean 'howler' so perhaps 'mistake' could also mean 'howler'). I'm not certain of the 'big' bit.
'doctor who hands over rose finally' is the wordplay.
'doctor' indicates an anagram.
'hands' becomes 'lr' (abbreviations for left and right).
'over' is an insertion indicator.
'finally' says to take the final letters.
The final letter of 'rose' is 'e'.
'lr' placed around 'e' is 'ler'.
'who' anagrammed gives 'how'.
'how'+'ler'='HOWLER'
Can you help me to learn more?
(Other definitions for howler that I've seen before include "Glaring error" , "Schoolboy error - wolf?" , "A monkey; a bad mistake" , "Serious blunder" , "Glaring mistake made by schoolboy" .)