Can players activate Quick-Play spells or Traps as face-down monsters are flipped face-up in battle?

Question

1. Player A's monster attacks player B's face down monster.
2. Both players decided not to chain the attack while monster is still face down
3. Monster is flipped face up, which is Kelbek
4. Player A activates Quick-Play spell Forbidden Chalice on player B's Kelbek so its effect is negated.

Question: Is player A allowed to activate Quick-Play spell after the monster is flipped face up?

Kelbek:

A monster that attacks this card returns to the hand. Damage calculation is applied normally.

Forbidden Chalice:

Target 1 face-up monster on the field; until the end of this turn, that target gains 400 ATK, but its effects are negated.

Answer 1

It Depends On What the Card Does.

So, keep in mind that because the monster is being flipped face-up in battle, it means that we're in the damage step at the time of the flip. Because of this, there are some restrictions on what kinds of cards can be activated. A card/effect may only be activated during the damage step if:

• It is a counter-trap card
• Its activation is mandatory
• It negates the activation of a card/effect (Note Activation, not Effect of)
• It directly modifies the Attack/Defense of any monster(s)

Forbidden Chalice happens to hit one of the criteria here (modifies ATK/DEF), so it can be activated in the given scenario. If, on the other hand, one wanted to use Breakthrough Skill, one would not be able, since it does not meet any of the above criteria.

Answer 2

Yes, that is possible. There's a few things to note here though.
From the website of Konami, this is what happens before damage calculation (so during the damage step)

• If the monster being attacked is face-down, flip it face-up. Then, cards or effects that modify ATK/DEF can activate. If the monster has a Trigger Effect that activates by being flipped face-up, it does not activate yet.

This means that after Kelbet has been flipped face up, 2 types of cards/effects can still be activated. Effects that alter the ATK/DEF of a monster or cards that negate the activation of a card.

So if Forbidden Lance only had the negation effect, you wouldn't be able to activate it. However, since it also changes the monsters ATK, you can activate it during the damage step, after the monster has bene flipped face-up.