a smaller size and body weight....

[birgit33]

"A smaller size and body weight means they can move easier." Which adjective modifies "weight" : is it "smaller" or "body"?

[bhaisahab]

"A smaller size and body weight means they can move easier." Which adjective modifies "weight" : is it "smaller" or "body"?

It's poorly written. Where did you find it?

[BobK]

It's poorly written. Where did you find it?

Perhaps birgit33 might think about why.
(The first problem is the one that made you post the question. But there are others.)

b

[SoothingDave]

Both "body" and "smaller" modify "weight." Or you can consider "body weight" to be a compound noun.