The most common and most likely answer to this crossword clue is the 6 letter word BOXING
I've seen this crossword clue in The Times
B
O
X
I
N
G
More clues leading to the result BOXING
- In such activity bell sounds — seconds out, round eleven
- Pupil once turning eleven, no good for sport
- Noise coming from trampolinist about unknown sport
- Packing in sport
- House not entirely accepting animal sport
- Putting in case for physical sport
- Nothing wrong in gambling game, almost a sport
- Fight packing them in
- Packing container holds neat opener for gift
- Sport on telly is not principally golf
Buddy explains!

The straight part
We know that "sport" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sport = boxing.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 BOXING mean?
BOXING verb- To place inside a box; to pack in one or more boxes.
- Usually followed by in: to surround and enclose in a way that restricts movement; to corner, to hem in.
- To mix two containers of paint of similar colour to ensure that the color is identical.
- To make an incision or hole in (a tree) for the purpose of procuring the sap.
- To enclose with boarding, lathing, etc., so as to conceal (for example, pipes) or to bring to a required form.
- To furnish (for example, the axle of a wheel) with a box.
- To enclose (images, text, etc.) in a box.
- To place a value of a primitive type into a corresponding object.
- To strike with the fists; to punch.
- To fight against (a person) in a boxing match.
- To participate in boxing; to be a boxer.
- A sport where two opponents punch each other with gloved fists, the object being to score more points by the end of the match or by knockout, or technical knockout.
- To place inside a box; to pack in one or more boxes.
- Usually followed by in: to surround and enclose in a way that restricts movement; to corner, to hem in.
- To mix two containers of paint of similar colour to ensure that the color is identical.
- To make an incision or hole in (a tree) for the purpose of procuring the sap.
- To enclose with boarding, lathing, etc., so as to conceal (for example, pipes) or to bring to a required form.
- To furnish (for example, the axle of a wheel) with a box.
- To enclose (images, text, etc.) in a box.
- To place a value of a primitive type into a corresponding object.
- To strike with the fists; to punch.
- To fight against (a person) in a boxing match.
- To participate in boxing; to be a boxer.
- Material used for making boxes or casing.
- Casing.
- Automatic conversion of value types to objects by wrapping them within a heap-allocated reference type.