In English near future is often replaced by the present: I will be leaving tomorrow -> I am leaving tomorrow. In this context in Russian near future can also be replaced by the present, or if the future is very near, it even can be replaced by the past. Всё, я пробегу. -- That's all, I'll be leaving now. Всё, я убегаю. -- That's all, I'm leaving. Всё, я побежал. -- That's all, I'm gone! (all mean the same) "бегать" in this context is replacing "ходить", to make it sound more lively.

я побежал = I'm leaving you, bye я побежал = to start running