The Messenger of Allah ﷺ prohibited throwing pebbles (in sport) saying : game is not caught by such means. Neither is an enemy injured, but it may sometimes put out an eye or break a tooth.  

نَهَى رَسُولُ اللَّهِ ﷺ عَنِ الْخَذْفِ قَالَ إِنَّهُ لاَ يَصِيدُ صَيْدًا وَلاَ يَنْكَأُ عَدُوًّا وَإِنَّمَا يَفْقَأُ الْعَيْنَ وَيَكْسِرُ السِّنَّ