Safeco Field in Seattle has a nice mothers lounge (nursing room) on the Main Level in section 128 Near Guest Services. The stadium welcome all nursing mothers to use it during game times or special events.
Also baby-changing tables are located in most restrooms throughout the ballpark.
Mom Jenni wrote: "I have to say the SafeCo Field Park is awesome because they had a mother's lounge with recliners, TVs (to watch the game), changing tables and more. I walked in there and never saw so many boobs. Great to know I wasn't the only breastfeeding mom in the park and that they created a space for it."