Its simple. The people slagging him off are the type that cant see the game of football except the flashy bits. They can only judge a player by his goals, and by the number of times he nutmegs the defender. What they dont see is when a player makes good use of space, shows well for his teamates, makes good runs, or makes good passes unless it literally is the last pass. What they dont realize is the third to last pass is almost as important as the last pass. For example, rolling the ball out wide slowly and behind your winger is a pass that often times stops an attack and keeps it from continuing one step ahead of the defense.
Klaassen is not and will never be the player who dribbles past 4 defenders. What he is is the prototype of a team player, sees space well, gets himself in good positions to help out teamates, passes the ball quickly and well to them, and then immediately goes into dangerous spaces. He will not create goals by himself. Right now we have an offense that is learning how to play with eachother, and that hurts his game. Once the offense starts to gel and understand eachother it will hit at the heart of his game, and you will see his stride.
And for all of that, the last 2 goals we have scored, to beat Stoke and to send us through in the Europa league were both set up by Davy. He and DCL are the only players to be instrumental in 2 of our 3 goals so far this campaign. He got the assist against Ruzomberok, and he made the run that left Wayne Rooney in acres of space against Stoke. Would be sheer madness, at a time when our offense is not hitting well, to leave off one of the 2 players most responsible for what it HAS produced.
