German fans again protested against Monday night football, which is proving unpopular in the Bundesliga, while Bayern Munich extended their lead despite dropping points.

In Saturday's goalless draw in Munich, Hertha Berlin's defence again frustrated Bayern's star-studded attack.

Ageing winger Arjen Robben is still fuming about dropping down the pecking order, but that anger drew praise from the man who picks the team, head coach Jupp Heynckes.

Here are five things we learned from the latest round of Bundesliga games.

Large numbers of Borussia Dortmund's fans boycotted Monday's 1-1 draw against Augsburg, but coach Peter Stoeger refused to blame the result on the protest.

Home games are normally 80,000 sell-outs, but only 54,000 fans turned up in Dortmund.

The protest was another blow aimed at the German Football League (DFL) who are experimenting with Monday kick-offs this season.

Dortmund's south stand, normally packed with 24,500 fans, was half empty leading to an eerie atmosphere.

That was after Eintracht Frankfurt fans pelted the pitch with tennis balls in last Monday night's game against RB Leipzig.

Dortmund's players commented on the absent fans, but Stoeger refused to use the protest as an excuse.

"Many clubs in Germany would be happy if they had 54,000," said Stoeger.

"To say you can only play football well in front of 80,000 would be a cheap, simple excuse."

Robben cuts a frustrated figure at Bayern, but Heynckes has played down talk of a rift.

The 34-year-old is out of contract in June and still fuming about starting the rout of Besiktas on the bench last week behind Thomas Mueller.

However Heynckes understands where the Dutchman is coming from.

"I was just like him as a player," Heynckes, 72, told German daily Bild.

"He would never have had such an awesome career if he hadn't been the character he is.

"I've seen so many young, highly talented players who never learned to work so professionally and practise so passionately.

"That's what Arjen does - he's a role model."

Berlin head coach Pal Dardai knows how to frustrate Bayern.

Hertha's 0-0 on Saturday was Berlin's third straight draw against Munich -- the best recent record of any league club against the runaway leaders.

"I have been hunting for the book 'How to beat Bayern', but in the mean time, I found 'How to stay unbeaten' and that's not so bad," joked Dardai.

A string of saves from Berlin goalkeeper Rune Jarstein and dogged Hertha defence denied Bayern, despite 19 shots on goal, but Munich are still 19 points clear in the table.

However, Bayern's recent below-par results against Berlin could be blamed on Champions League hangovers.

Saturday's draw came after Munich thrashed Besiktas 5-0 last Tuesday in the last 16, first leg.

In October, Bayern threw away a two-goal lead in a 2-2 draw in Berlin in the wake of their 3-0 group stage thumping at Paris Saint-Germain.

After netting five goals in his first three games at Borussia Dortmund, Michy Batshuayi, on loan from Chelsea, has now failed to score in his last three matches.

The Belgian striker produced just one shot on goal against Augsburg and rarely troubled the defence in a below-par display.

As the Sky match commentator observed, "he seems to be living off his reputation from when he first arrived".

Germany winger Marco Reus gave Dortmund an early lead, but Batshuayi failed to spark as Augsburg came back and equalised through 19-year-old defender Kevin Danso.

"That's not what we want to see, we might as well have dismantled the goals," moaned Stoeger after Borussia's Batshuayi-led attack stuttered in th second half.

Second-from-bottom Hamburg are again facing relegation, but have huge problems on and off the pitch.

Their 1-0 defeat at Werder Bremen on Saturday left them eight points from safety.

They can expect heavy German FA (DFB) sanctions because the match was halted three times after Hamburg fans fired flares onto the pitch.

"These aren't fans, they're people who want to destroy football," fumed Hamburg president Heribert Bruchhagen.

Police expect more trouble for Saturday's relegation battle at home to Mainz.