The most common and most likely answer to this crossword clue is the 7 letter word BATTLES
I've seen this crossword clue in The Times
B
A
T
T
L
E
S
Buddy explains!

The straight part
We know that "Waterloo, Stamford Bridge, say?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case waterloo, stamford bridge, say? = battles.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.
What does BATTLES mean?
BATTLES noun- A contest, a struggle.
- A general action, fight, or encounter, in which all the divisions of an army are or may be engaged; a combat, an engagement.
- A division of an army; a battalion.
- The main body of an army, as distinct from the vanguard and rear; the battalia.
- To join in battle; to contend in fight
- To fight or struggle; to enter into a battle with.
- To nourish; feed.
- To render (for example soil) fertile or fruitful