The years they won Bundesliga were the years they were best defensively. In 2011 they allowed 22 goals against (best in league) and in 2012 they allowed 26 goals against (2nd best in league).
The next two years they allowed 42 and 38 goals and finished a mile behind Bayern. 25 points and 19 points back. Even though they scored more goals in these seasons.
Ultra-defensive play isn't required, but defensive solidity at the back is. Borussia is a perfect example of it by seeing how far they fell off as soon as they started leaking goals at the back.
The next two years they allowed 42 and 38 goals and finished a mile behind Bayern. 25 points and 19 points back. Even though they scored more goals in these seasons.
Ultra-defensive play isn't required, but defensive solidity at the back is. Borussia is a perfect example of it by seeing how far they fell off as soon as they started leaking goals at the back.
