It would help to know what hawks but as a quick reply, yes some individuals of some hawk species are aggressive in defence of their nest, so that is the likely answer.
The Brown Goshawk is the likely one and the Peregrine Falcon also puts up a fuss near their nest but I don’t know that they actually harm people.
Some local governments will put up signs that say something like “beware swooping bird”. Although these are normally for magpies, there is a trend for the signs not to mention magpies, so they can be used for other birds and also so that they don’t get souvenired by Collingwood football fans.
Philip
