I stopped by a high school baseball field late last week. As you can see, there was a lot of slack in the bottom of the net. The bottom of the net was connected to the cable by zip/cable ties.
It is common to purchase the net that is a little larger than the opening. The best way to adjust tightness of the net is to lace the cable using #30 tarred treated twine. In this application, the J&D Turf team gathered the net along the cable and laced the net to the cable. This will eliminate cable tie breakage. Note how the net is consistent across the bottom cable and every piece of the net is square.
If gathering the net is not an option, you can always trim the net to "fit to size."
Look for future posts on backstop nets and a case study from a high school project.
Go to j-dturf.com to learn more about J&D Turf.