The following is from a popular modern retelling of Shivaji's story. Nonetheless, till we get better details, it serves to explain why he attacked forts belonging to his sovereign. It also helps to explain why he waited thirty years into his career to proclaim himself as king. Legally, all this time, he would have been a vassal of Bijapur.
Shivaji's major forts lie mainly west of the City of Pune [Poonay, Poona].
From a combination of the two circumstances, it also becomes clear why in most historical accounts Shivaji is referred to as a "chieftain" and not a king.
The illustration and the quote below are from http://www.indhistory.com/shivaji.html. We've slightly edited the quote for grammar.
[Bijapur did not permit Shivaji's father to control any fort. As a youngster, the charismatic Marattha gathered around him a band of men who were ready to follow him to any adventure.]
| In his early years, his band attacked the mountain fort of Torna about twenty miles from Poona. He took control from the fort as Governor. It was characteristic of him immediately to send word to the King of Bijapur, that he had done this purely in the king's interest as the ex-governor was not given all the revenue due to the king. This brought more time, and Shivaji used this technique of cunningness to conquer more and more such forts. The king eventually ordered Shivaji to stop these activities. But Shivaji knew that by now the whole region was behind him and thus ignored any warnings from the King of Bijapur. |