Hi In the example, the phrase 'up and down' implies horizontal movement. Usually, up and down mean vertically, but here, up and down THE FIELD,means something like to and fro, thus meaning horizontal. Summing up, unless a plane ( like the field here ) is mentioned, up and down is used for altitude, but if a plane is mentioned, it means something like going horizontally, in one direction and then in the opposite.
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