user-1: This is taken from a rapid game where my opponent threw me by playing 8. g3, coming out of book in the 4. e3 Slav:
[FEN ""]
[StartPly "17"]

  1. Nf3            Nf6           
  2. c4             c6            
  3. d4             d5            
  4. e3             Bf5           
  5. Nc3            e6            
  6. Nh4            Bg6           
  7. Nxg6           hxg6          
  8. g3

I didn't keep a gamescore (it was at work during a lunch break), but I remember at this point I could think of no constructive plan at all (I played 8...Bb4 and ended up playing 2 knights vs. 2 bishops with a cramped game).
My question is, what should black have played on move 8 and why?

user12540: There is nothing to worry about when an opponent makes a surprise move in the opening and you are unaware of it. 
g3 is not a move that you would be blown away by it. Just follow basics to develop your pieces. Black has the open h-file. Nbd7 and then a centre break of e5 should follow next course. The bishop on f8 comes to b4 or d6 and knight comes to e4. I think black has a better piece activity and should have gone on to winning the game.

user11609: I see no reason to ?! mark. 8. g3 is good book move and standard way to limit opponent's play with open h-file. The most flexible move by far is 8...Nbd7 after it. After 9.Bg2 dxc4 should be good. But again, 4...Bf5 is no refutation of slow Slav and 5...Bg6 is in my opinion less challenging than 5...Be4, while there's nothing wrong with 8.g3. Don't expect you have guaranteed equality in this line. Once I played the NN vs. BB game in similar line and it is suffer, even if computer says it is OK. I was always somewhat worried about 4...Bf5 as white, but as black, I played 4...Bg4 every single time :-) 

-1: <p>This is taken from a rapid game where my opponent threw me by playing 8. g3, coming out of book in the 4. e3 Slav:</p>

<pre><code>[FEN ""]
[StartPly "17"]

  1. Nf3            Nf6           
  2. c4             c6            
  3. d4             d5            
  4. e3             Bf5           
  5. Nc3            e6            
  6. Nh4            Bg6           
  7. Nxg6           hxg6          
  8. g3
</code></pre>

<p>I didn't keep a gamescore (it was at work during a lunch break), but I remember at this point I could think of no constructive plan at all (I played 8...Bb4 and ended up playing 2 knights vs. 2 bishops with a cramped game).</p>

<p>My question is, <strong>what should black have played on move 8 and why?</strong></p>
 12540: <p>There is nothing to worry about when an opponent makes a surprise move in the opening and you are unaware of it. </p>

<p>g3 is not a move that you would be blown away by it. Just follow basics to develop your pieces. Black has the open h-file. Nbd7 and then a centre break of e5 should follow next course. The bishop on f8 comes to b4 or d6 and knight comes to e4. I think black has a better piece activity and should have gone on to winning the game.</p>
 11609: <p>I see no reason to ?! mark. 8. g3 is good book move and standard way to limit opponent's play with open h-file. The most flexible move by far is 8...Nbd7 after it. After 9.Bg2 dxc4 should be good. But again, 4...Bf5 is no refutation of slow Slav and 5...Bg6 is in my opinion less challenging than 5...Be4, while there's nothing wrong with 8.g3. Don't expect you have guaranteed equality in this line. Once I played the NN vs. BB game in similar line and it is suffer, even if computer says it is OK. I was always somewhat worried about 4...Bf5 as white, but as black, I played 4...Bg4 every single time :-) </p>
