Upright meaning
Hail, the coldest of grains. A sudden storm you did not choose, but hail melts into water and water feeds the field. Disruption now, growth after.
Reversed (merkstave)
Hagall looks the same either way up, so it has no reversed meaning. Read it upright every time.
A question to sit with
What could grow from the thing that has just knocked you flat?
Its ætt
Hagall belongs to Hagall's ætt, the runes of forces outside your control and the growth they force.