The most common and most likely answer to this crossword clue is the 4 plus 4 letter word BUMP INTO
I've seen this crossword clue in The Guardian
B
U
M
P
I
N
T
O
More clues leading to the result BUMP INTO
- Light upon and behind horse
- Encounter inferior bit of beer, nothing more
- Encounter worthless horse
- Meet by chance behind horse
- Meet vagrant on horse
- Meet tramp on horse
- To come across undrinkable beer’s nothing
- Come across beggar having casual drink in the middle of Stoke
- Encounter tramp with American piebald
- Happen to meet tramp needing drink by front of Odeon
Buddy explains!

The straight part
We know that "Meet by chance/Meet by chance" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case meet by chance/meet by chance = bump into.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.