NO. Sports cards should not be shipped via media mail through USPS.
Media Mail is cheap, but it has many restrictions. According to the USPS, if it isn’t bound and at least 8 pages, it does not fall under Media Mail, and USPS can and will open and inspect packages that it thinks may violate it’s terms. Often, media mail packages that violate terms will be returned, or delivered with a requirement to the addressee to pay the difference in shipping.
Don’t ship your trading cards by Media Mail just to try to save a couple bucks, it’s not worth it. Always ship cards First Class or Priority.