* this dent - "this" is a demonstrative adjective, specifying which dent.
* my door - "my" is a possessive adjective, showing ownership.
* that ball - "that" is a demonstrative adjective, specifying which ball.
* on green grass - "green" is a descriptive adjective, telling us the color of the grass.
Therefore, there are four adjectives in the sentence: this, my, that, and green.