NEW YORK (TheStreet) -- Coventry Health Care was the worst-performing stock in the S&P 500 on Friday morning. The S&P 500 was rising 1.09 points, or 0.08%, to 1,401.07. Shares of Coventry Health Care fell 10.28% to $29.32. The health care company reported Friday first-quarter earnings of $170.7 million, or $1.20 a share, up from year-earlier earnings of $110.2 million, or 73 cents a share. ... Click to view a price quote on ^GSPC.