When the Mariners return to Seattle 's Safeco Field for their April 8 home opener an upgrade featuring the largest HD video board in Major League Baseball .
Their April 8 home opener is an HD - video upgrade four years in the making will finally be complete .
When the Mariners return to Seattle 's Safeco Field for their April 8 home opener , an HD - video upgrade four years in the making will finally be complete , an upgrade featuring the largest HD video board in Major League Baseball .