I, and quite a few of my playing partners, have taken the same tennis bags on four different airlines over the last two years. Never been questioned about it.
Just trying to give an example to a concerned traveler and my bag actually takes up much less room than many of the foot lockers I have seen squeeze down the aisle.
It sits upright in the back of the overhead space and bags can be placed in front of it (4 inched wide). It is the only bag I take on board.
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