The most common and most likely answer to this crossword clue is the 6 plus 7 letter word SEASON TICKETS
I've seen this crossword clue in The Guardian
S
E
A
S
O
N
T
I
C
K
E
T
S
More clues leading to the result SEASON TICKETS
Buddy explains!
The straight part
We know that "These in stock? Sees at ground" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case these in stock? sees at ground = season tickets.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.