COSTA MESA, Calif. (AP) — The Los Angeles Chargers concluded the first week of organized team activities with first-round pick Zion Johnson signing his rookie contract. The guard got the standard four-year deal with the team holding a fifth-year option. The 17th overall pick in last month’s NFL draft, Johnson is expected to start at right guard when the Chargers open the season at home against the Las Vegas Raiders on Sept. 11. The Chargers have signed six of their eight draft picks. Safety JT Woods, a third-round pick, and running back Isaiah Spiller, a fourth-round selection, remain unsigned.