Why try in a match after your team is guaranteed to pass the group stage

Question

I was thinking about Group D (standings after two matches) in the world cup this year, and as it stands now, Croatia has a big lead:

          W T L  pts goal-difference
Croatia   2-0-0   6        +5  
Nigeria   1-0-1   3         0  
Argentina 0-1-1   1        -2
Iceland   0-1-1   1        -3

The next two matches are Nigeria vs Argentina and Iceland vs Croatia

In my mind, Croatia has very little to gain from winning their match. The only team that can tie them in points is Nigeria, but in their next match, Argentina will be playing to win (since they still have a chance to take second in the group), so Nigeria probably won't get the goals to take first in the group on a tie-break based on goal difference.

In my mind, the best strategy for Croatia here is to play to avoid injuries and cards so that all of the players start the knockout phase fresh, even if that means benching the key starters and losing the match.

Is there anything that prevents Croatia from using this strategy, or is this common in the World Cup?

Answer 1

The short answer is that Croatian team can choose to do so and nothing prevents them from giving chance to players who don't appear often in the starting lineups of Croatian team to play in the last match of the group.

Indeed, in order for Croatia to finish second, they need to lose to Iceland with a goal difference of at least 2 or 3 while Nigeria win over Argentina with a goal difference of at least 3 or 2. Besides that, in the case of equal points and equal goal difference, Nigeria still has to have more goals scored or otherwise they will finish second as they lost in the head-to-head match against Croatians. So, Croatians are in a very comfortable position and can choose to do so and here are the main factors which will affect the coach's decision on the next matchday lineup:

• There's still a risk to face the winners of group C (favorites France most probably) instead of Denmark or Australia if they somehow finish second.

• World Cup is a unique tournament, in which all players (including usual starters) want to participate in every match no matter the importance of the result of the match.

• Injuries and the rest time, which have already been mentioned in the question. Croatian's Round 3 game will take place 5 days after their Round 2 game. And their Round of 16 game will take place 4 or 5 days after their Round 3 game. This is a little bit dense graphic with training sessions in between, so some rest for key players is very important.

• Another minor fact would be the removal of the first choice substitution center-forward Nikola Kalinić from the squad, so some rest for other forwards like Rebic or Mandžukić is inevitable.