how to fight back e4 by a5

Can some body help mee ?

You want to play a5 or somebody played it against you?

Why give white a nice pawn duo?

to try to undermine it later like most hypermodern openings?

And a5 is going to help you undermine the center?

Yes. The opening 1. e4 a5 2. d4 Ra6 3. Bxa6 Nxa6 opening is very strong at undermining the center.

Best way to neutralize center is 1. e4 f6 2. d4 g5.

After Qh5 then the center is unimportant.

a5 sucks.  Who wants to play it against me?

Preston Ware, a strong master at the time, played this opening in the New York Trounament of 1880, both as white and black. It's listed as the "Corn Stalk Opening."

some masters played without some of their pieces, up to their queen ?

This is one of my games i got tilted after flagged twice in completely winning position against same opponent. I wanted to say him i am much better by sacrificing my piece right at the beginning. Fortunately he even didnt make it hard for me, just tried to exchange queens after then and found himself in situation either he loses a piece back or losing his queen.

Fifty years ago I played against a chess master together with over twenty others in a simultaneous game. He lost one game with the e4 a5 opening - he wasn't equipped to fight back. I remember talking to his apponent who told me how important it was to study a few diverse black openings.