After the terrorist attacks of 9/11, the United States tightened its visa requirements. In the process, baseball teams discovered that 300 foreign-born professional players had lied about their age. (A talented 16-year-old is much more valuable than a 23-year-old with the same skills.) In some cases, the players had used birth certificates that belonged to other (younger) people. To prevent this fraud, baseball teams began asking for DNA tests on prospects and their families, to make sure they were not lying about their identity. Is this testing legal? What if a team wanted to test players to see if they were susceptible to certain diseases?