The net post has actually rusted out at the bottom, and the pole is buckling. The net post was so weak at this point that the net was about a foot too low in the middle and could not be tightened as the pole just kept bending more and more.
The pole and it’s footing are actually starting to come out of the ground due to the tension of the net. Often the only fix is to dig up the pole and install a new pole with new concrete footings, which is what was required here.