Stavanger Bay rather have been killed by that beast than be saved by a half-breed

His play grew rougher and rougher to the point where Lagertha's tail lost its wag and her smile fell flat. Still, she did not stop engaging him. It had lost the air of mirth, more as if she had something to prove to him. Even if the Viking was unsure just what her point was, she would prove it.

Some part of her rationalized that he could not truly hurt her, maim her in some incomprehensible manner. Skellige needed able bodied wolves and for them to go about permanently injuring the other would go against that need. Tetsubo would recognize this somewhere inside, she told herself. And whether or not it was true, Lagertha believed. 

Despite the actions turning more violent by the second, Lagertha did not growl at him nor did she snap or hurt him. Her actions remained collected, gentle sparring nips and taps. The Valkyrie would not hurt a comrade, no matter how rough he treated her.