Mediocre writing before editor initially runs tabloid? (5)
'tabloid?' is the definition.
(I've seen this in other clues)
'mediocre writing before editor initially runs' is the wordplay.
'mediocre writing' becomes 'pap'.
'before' says to put letters next to each other.
'initially' suggests taking the first letters.
'runs' becomes 'r' (cricket abbreviation).
The initial letter of 'editor' is 'e'.
(Other definitions for paper that I've seen before include "First wedding anniversary", "Alternative to scissors or stone?", "Written essay", "Maybe Times", "Threat that seems powerful (but is just a pussy cat!)".)