"The run was a little out of balance here last year," observes Larry Csonka in a tactful bit of understatement. "And that's where I figure in." The figure that lured Csonka to the Giants was $1.5 million, and he already has helped the team get a return on its investment: the new 76,500-seat Giants Stadium in the New Jersey meadowlands has been sold out for the schedule. All the Giants want from the 240-pound Csonka is what he consistently gave the Miami Dolphins: hard, inside, 1,000-yards-a-year running, solid blocking and a contagious winning attitude. "On third and three now, the linebackers will have to freeze for a moment," says Quarterback Craig Morton. "Last year they dropped to their pass coverage right away because they knew we couldn't run and had to throw."