Coach following Everton's lead certainly causes tension for viewers (9)
I believe the answer is:
eyestrain
'tension for viewers' is the definition.
'coach following everton's lead certainly' is the wordplay.
'coach' becomes 'train' ('train' can be a synonym of 'coach').
'following' means one lot of letters go next to another.
'lead' says to take the initial letters.
'certainly' becomes 'yes' (I've seen this before).
The initial letter of 'everton' is 'e'.
'e'+'yes'='eyes'
'train' put after 'eyes' is 'EYESTRAIN'.
'causes' is the link.
(Other definitions for eyestrain that I've seen before include "Reader's problem" , "It might cause pupils problem" , "Tiredness when reading" , "You're looking too hard for this" , "Vision tiredness" .)