You will need to fill in the low spot with the same material that is used throughout the entire infield. First start with a soil test to determine your sand/silt/clay mixture in your field and be sure that the material you are adding to the low spot matches.

Then, incorporate about 20% percent Turface® into the mix in order to effectively absorb water during rains.

Scrape out any loose infield mix in the low area, and begin filling the space with the new infield mixture. Pack and level the area so the low spot is removed, then topdress to match the rest of the playing surface.