Denver Nuggets swingman Will Barton will not agree to a contract extension this offseason and will test unrestricted free agency in the summer of 2018, league sources tell ESPN. Sources say the Nuggets anticipated Barton's decision, made in an attempt to maximize his earning potential during the prime of his career.  Barton, 26, is one of the league's premier sixth men. He will be entering the final year of his three-year, $11 million contract in the 2017-18 season. His $3.5 million annual salary can be seen as a sizable bargain given his production. In Barton's first two full seasons with the Nuggets, he averaged 14.4 points and 13.7 respectively and shot a career-high 37 percent from 3-point range in 2016-17. Under the new collective bargaining agreement, players who are on three-year contracts are eligible to sign an extension after the second-year anniversary of the pact. If Barton chose to go the extension route, his salary would be the greater of 120 percent of his...