ts% = .5 * pts / (fga + .44*fta) If you know points, fga, and fta splits, you can calculate ts% splits.
I take a much easy equation to measure offensive efficiency without calculator, PTS - FGA - FTA, large value means more efficiency.
Adjusted Field Goal Percentage on ESPN looks also very reasonable to me. http://espn.go.com/nba/teams/stats?team=hou
So a guy who took no shots but went 10-12 from the line would have a -2? Anyone can make up an equation, but yours doesn't make any sense to me. There's no reason to use FTA as equivelant to FGA. Maybe if you divided FT by 2 you'd have something...
I haven't found a player took no shots but went 10-12 so far. The method is not perfect, but simple. The reason to use that equation is that I assume the standard for a player could make 50% of his shots and all of his free throws. This standard is slightly high, but is easy to calculate. Applied it to any team, it generally gives a pretty reasonable evaluation on players.