The most common and most likely answer to this crossword clue is the 10 letter word STEVEDORES
I've seen this crossword clue in The Guardian
S
T
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More clues leading to the result STEVEDORES
Buddy explains!

The straight part
We know that "They load" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they load = stevedores.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 STEVEDORES mean?
STEVEDORES noun- A dockworker involved in loading and unloading cargo, or in supervising such work.
- To load or unload a ship's cargo.