Dictionaries define grammar as the rules and explanations which deal with the forms and structure of words (morphology), their arrangement in phrases and sentences (syntax), and their classification based on their function (parts of speech).
Your sentence probably looks something like this:
1. The man is throwing the ball.
2. The pitcher is going to throw the ball
You might even have written:
3. The ball is being thrown by the pitcher.
Whatever you wrote, it probably include the word ball, the action throw, and a word that meant a man. You certainly didn’t write:
Ball throwing man the the is
That wouldn’t make sense and people hearing or reading your message would be confused. You wrote the sentence the way you did because you already know and use the basic rules of grammar.
Here’s what probably happened at lightning speed in your head. First, you saw the picture, and your brain understood the ideas the picture presented. Then you thought the names (vocabulary) for the things you just saw and arranged them (syntax) in an understandable order. Finally, you translated each sound in each word into letters (spelling) and wrote the entire sentence. In fact, you probably started your sentence with a capital letter and ended it with a period (punctuation). You see you really do know lots about grammar!