Adjectives are the words which qualify or modifies a noun or pronoun in a sentence. It describes them by providing a description of its size, origin, color and so on. For example, good, bad, old, brown, broken etc.
In the above phrase, The great Jackie Robinson won the MVP in 1949, the adjective is 'The great.'
It qualifies the noun<em> 'Jackie' </em>and describes him to be <em>'great.'</em>
The appearance of Tybalt foreshadows Romeo's eventual death as he narrowly escapes it at Tybalt's hands. It creates a sense of impending danger for Benvolio, Mercutio and the audience as it is the first indication that Romeo is doomed.