Are they throwing the grapes at: each other? Other soldiers? The targeted officers?
This. All officers? Other people? Animals? Buildings? Vehicles? The ground? Are they thrown with great force?
Enough. Great precision?
Yes. A great distance?
No. Are they thrown in a manner that makes it hard to know who threw?
From the point of view of the concerned officers, yes. do they splatter?
Yes. Make stains?
Probably. Bounce? Annoy someone?
Yes. After being thrown, are they inedible to humans?
Probably. Relevant how many are thrown? If so, less than 5? 10?
Assume around this. 50? 100? More?
SPOILER
In the linked "Willie and Joe" cartoon by Bill Mauldin (hence the puzzle title), a convoy of American soldiers passes through a French town, whose inhabitants are passing out fruit, wine and flowers to the soldiers. Two officers in a jeep have been struck several times by what appear to be grapes and plums, which are being thrown at them by privates in the truck behind them. One says to the other, "My, sir, what an enthusiastic welcome!"
https://i.postimg.cc/fWVNkKzt/My-sir.png