Strange defensive opening

My friend always plays this. I was wondering how I can exploit the weakness in the centre during this opening.

1. g3...

2. Nf3...

3. Bg2...

4. 0-0

Here's a game I played against him recently. I know neither of us played a great middlegame, but is this opening good enough to exploit the weakness in the centre?

Ok the technique your friend is using is called putting the bishop in fianchetto (translates as putting it in the flanks), and it wants to control the long diagonal so that the bishop is most useful. If you manage to swap something off for that bishop then the defence becomes weak so that is worth bearing in mind. It is also useful to block the bishops converage of the long diagonal with pawns. So on move 4 you could have played Pe5 to block the bishop in, and to move the knight out of its comfortable square. But you have the right idea, generally try and occupy the centre and push on forwards through the centre of the board while your friend tries to attack you from the sides.

the opening your friend is playing transposes in the pric defense you take more control over the center by playing f4 before developing your kingside knight. Opening might look like this.

you could also play this,  now blacks position is really cramped  and he is behind in development. 

In the second diagram 5. f4 might be better than 5. c5?! simply because it doesn't give up the d5 square.

after 5. f4 d5 white loses control of the d5 square anyway

<sparta> Agreed. In fact, any development move would be better.

 <KrazyFK> in your game, did you not notice your e4 pawn was unprotected on moves 3 and 4? you should have protected it with Nc3 or by pushing it to e5. This is a "pircs defense", and while I'm not very fond of Bc4 (which allows black to gain moves by attacking it with pawsn) it is, nevertheless, playable.

<pvmike> the f4 plan is not the "best" (which you insinuated by only showing it) way to handle the the pirc (though it is a "good" way, and a good agressive option.) There are other ways, such as positionally with Nf3(without f4) and Be2), agressive with Be3, f3, and Qd2(with plans of Bh6 and h4), and some other weird stuff. 

  

oh yeah I definitely agree, I didn't intent to imply that the f4 plan was the best way to play against pirc, I don't even play the Austrian attack against the Pirc, I stick with the classical system playing 4.Nf3, I suggested the Austrian Attack because KrazyFK said he wanted a way to exploit Blacks weakness in the center, playing f4 does just that. But I still think the second line I gave is solid, other moves are also strong, but I don't see a downside with 5.c5. 

I did notice my pawn was unprotected, but I also knew he wouldn't touch it until his king was safely castled (predictability is a terrible weakness).

in the pierce defense, you usually play d6 first so that the e pawn won't attack the Knight on f6

KrazyFK wrote: I did notice my pawn was unprotected, but I also knew he wouldn't touch it until his king was safely castled (predictability is a terrible weakness).

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 play the board, not the man-Its not good to play chess using a person's habits. Any decent club-level player(and those stronger too of course) would snatch that pawn, play d5, and marvel at their new found stolen-loot. Sure, your opponent won't take it, but why are you practicing something your not intending to play against better players?