Why can't I declare a generic interface field without providing types?

Question

I'm making a weapon/shooting system so that each Hero will be provided with it's own logic at compile time.

An example would look like:

class MageHero : Hero {

    MageHero(){
        base(new SingleShotAttackStrategy>());
    }
}

class BowmanHero : Hero {

    BowmanHero(){
        base(new MultishotAttackStrategy>());
    }
}

Each strategy has it's own logic for spawning bullets. Then, when I call Hero's Attack(), attached logic would be executed.

To the point

I come from Java. In Java, I can do that:

// there will be a different attack input for different shot types (single shot, multi shot...)
public class BaseAttackInput{}

class SingleShotInput extends BaseAttackInput{
    public int x, y;
    public int dirX, dirY;
    public int bulletSpeed;
}

public interface IAttackStrategy<T extends BaseAttackInput> {
    void attack(T input);
}

// specific strategy for a single shot
public class SingleShotStrategy implements IAttackStrategy<SingleShotInput>
{
    @Override
    public void attack(SingleShotInput input) {
        // spawn one bullet from the input's data
    }
}

public class MultiShotStrategy{...}

public class Hero{
    public IAttackStrategy strategy;

    void initialize(IAttackStrategy strategy){
        this.strategy = strategy;
    }
}

void testHero(){
    Hero hero = new Hero();
    hero.initialize(new SingleShotStrategy());
}

In the equivalent code in C#, I can't do that:

public class Hero{

    // ERROR, This needs to have specified generic types!
    public IAttackStrategy strategy;

    // this aswell...
    void initialize(IAttackStrategy strategy){
        this.strategy = strategy;
    }
}

And then comes the fun, because I have to add generic parameters to the Hero class, and then, provide generic parameters in each subclass of the Hero class etc...

What to do?