All upset about a blob at the close of play, it's true (5)
I believe the answer is:
loyal
'true' is the definition.
(I've seen this before)
'all upset about a blob at the close of play' is the wordplay.
'upset' indicates anagramming the letters.
'about' is an insertion indicator.
'a blob at' becomes 'o' (I can't justify this - if you can you should give a lot more credence to this answer).
'the close of' indicates one should take the final letters (the letter which ends or closes the word).
The final letter of 'play' is 'y'.
'all' is an anagram of 'lal'.
'o'+'y'='oy'
'lal' going around 'oy' is 'LOYAL'.
'it's' is the link.
Can you help me to learn more?
(Other definitions for loyal that I've seen before include "Alloy (anag.)" , "Steadfast and true" , "Not perfidious" , "Staunch" , "Dedicated" .)