Does if effect your ability to fight if u r fighting in someone else's castle. It's a castle he's just taken over so he hasn't built anything on it yet.
How does fighting efficiency get effected when u're fighting in
1. Your own castle.
2. Someone Else's castle.

1. without any upgrades on the castle your defense increases by +5

with castle protection some points more
with castle defense even more
maybe someone has an idea about how much? i donīt know it atm

2.thereīs no effect on your fighting ability

i believe that it is 20% more defensive increase with castle protection and castle defence technologies, though i may be wrong on the castle protection. I am pretty sure though that this is the truth with castle defence. I think it may be against ranged only though, for the caslte defence... "20 % more defence against ranged troop types" or something like that...

Like Viva said +5 defense with no upgrades and these are the two updgrades you can get...

+ Castle Protection
Castle Protection prevents normal troops from taking over an empty castle.

+ Castle Defense
All troops within the Castle take 20% less damage from melee or ranged attacks.