Getting priority after putting a spell on the stack

Question

I have a two questions connected with priority and stack:

1. It's my turn, during the combat phase, after the declaring blockers step. Blockers are declared. At the Combat Damage step, I get priority and I pass. My opponent gets priority and decides to put a spell on the stack. Can I respond to him, adding my spell to the stack? And generally, do I always get a chance to respond after spell is put on a stack, independently from the situation?
2. Can I hold priority during opponent's turn? By hold i mean for example when my opponent in his turn cast an instant, i decide to respond, and now basically he would get priority again, and my question is can i hold it by telling that i hold and cast second instant after first one. I know that there is possibility to do it.

Answer 1

Yes, you can always respond when another player casts a spell or activates an ability. Steps or phases where players get priority only end if all players have passed priority in succession and the stack is empty. You will also get priority on opponents' turns.

The active player is the player whose turn it is.

116.3. Which player has priority is determined by the following rules:

116.3a The active player receives priority at the beginning of most steps and phases, after any turn-based actions (such as drawing a card during the draw step; see rule 703) have been dealt with and abilities that trigger at the beginning of that phase or step have been put on the stack. No player receives priority during the untap step. Players usually don’t get priority during the cleanup step (see rule 514.3).

116.3b The active player receives priority after a spell or ability (other than a mana ability) resolves.

116.3c If a player has priority when they cast a spell, activate an ability, or take a special action, that player receives priority afterward.

116.3d If a player has priority and chooses not to take any actions, that player passes. If any mana is in that player’s mana pool, they announce what mana is there. Then the next player in turn order receives priority.

116.4. If all players pass in succession (that is, if all players pass without taking any actions in between passing), the spell or ability on top of the stack resolves or, if the stack is empty, the phase or step ends.

Answer 2

Yes

All players must pass priority before something on the stack can resolve.

608.1. Each time all players pass in succession, the spell or ability on top of the stack resolves. (See rule 609, “Effects.”)

After your opponent puts a spell on the stack, it doesn't resolve until all players have passed priority. IE, before that spell resolves, you will get priority and can take any actions you could normally take at this time. (Obeying timing rules. Usually, this means you can only activate abilities and cast instants.)

In answer to if you generally always have a chance to respond before something on the stack resolves, yes. Again, 608.1 shows that all players receive priority between any time that something on the stack resolves. Note that you might not be the first person to receive priority.

Some effects will prevent you from taking actions when they are on the stack or as static abilities. (For example, spells with Split Second). However, even in this case, you still receive priority before they resolve. (Though there is typically little you can do with this priority.)

Special Actions, such as playing a land and morphing a creature, do not use the stack. As such, you are not given priority before they resolve.