Sprite Manager

I would set up a state engine and a counter :

 enum spriteState { Idle, FirstFrames, LoopFrames }
 
 var spritePlayState : spriteState;
 
 function Start()
 {
     // Set the state like this : 
     
     spritePlayState = spriteState.FirstFrames;
 }
 
 function Update()
 {
     switch( spritePlayState )
     {
         case spriteState.Idle :
             Idle();
         break;
         
         case spriteState.FirstFrames :
             FirstFrames();
         break;
         
         case spriteState.LoopFrames :
             LoopFrames();
         break;
     }
 }
 
 function Idle()
 {
     // do nothing, or just play first frame
 }
 
 function FirstFrames()
 {
     // Use your play script here to cycle between frames 1 and 11
     
     // from here you can also change states
     
     if (Input.GetKeyDown(Keycode.Space))
     {
         spritePlayState = spriteState.LoopFrames;
     }
     
     // or instead change state when frame reached 11 =]
 }
 
 function LoopFrames()
 {
     // Use your play script here to cycle between frames 12 and 17
     
     // then with another condition return to Idle state
     
     // spritePlayState = spriteState.Idle;
 }

This is probably too complex for what you are after, but anyway, here's a state engine =]